Discharge of sewage into the municipal sewerage system or into autonomous septic tank carried out through pipes by gravity. Therefore, it is important to observe the slope of the sewer pipes by 1 meter in accordance with the requirements of SNiP. A number of factors affect the normal operation of the drain system, from diameter and material to location: internal wiring or outdoor.

General information

The main task in the arrangement sewer system consists in configuring the pipeline in such a way that effluents, including liquid and solid fractions, pass without delay and without creating congestion and plugs. It is necessary to observe the slope of the pipes, along which, under the action of gravitational forces wastewater will immediately flow into the collector and further to the treatment plant.

Requirements for the organization of internal and outdoor sewerage, required slopes and other parameters are strictly stipulated in SNiP SNiP 2.04.01-85 “BUILDING NORMS AND RULES INTERNAL WATER SUPPLY AND SEWERAGE OF BUILDINGS” and SNiP 2.04.03-85 “SEWER. OUTDOOR NETWORKS AND STRUCTURES.

Behind the established norms is not a strict calculation, but the result of tests and observations. The nature of the drains and their consistency is not constant, and the sewage system must work without failures. It is necessary to exclude or minimize the settling of solids and sludge on the walls of the channel, to make sure that the sewer works silently, preventing reverse current and getting unpleasant odors back into the room.

It has been established that at a flow velocity of 0.7 m/s, water flows evenly and solid inclusions follow the flow of the liquid more easily, without lingering in one place. This is provided that the diameter is chosen so that with a normal number of drains for a given connection, they are filled by about 50-60%, but not less than a third.

The basic formula obtained empirically, based on observations, is:

where V is the effluent flow rate, H is the height of the effluent level in the pipe, d is the pipe diameter, K is the slope coefficient, the value of which is a reference value set depending on the pipe material.

K = 0.5 for plastic and glass.

K = 0.6 for other materials (steel, cast iron, asbestos cement).

The coefficient depends on the roughness inner surface and the resistance created by the fluid flow.

If the slope is too great, the water will drain quickly and solids will settle on the surface of the pipe, creating a blockage. With a large inclination, the water flow will be turbulent with whirling noise and increased air pressure in the upper part of the pipe, which will lead to breakage shut-off valves disruption of siphons or, at least, retraction of the water seal and the flow of gases from the sewer into the room. Cornering will form a build-up.

If the slope is too shallow or absent, then heavy fractions will have time to settle on the surface and eventually cause blockage. Since water cannot quickly overcome the entire route to the point of discharge, there will be an overflow when the next portion arrives.

It turns out two conditions for pipes to ensure the normal functioning of the sewer:

• The diameter is selected based on the average volume of drains.
• The slope is determined to provide an optimum flow velocity of 0.7 m/s.

Tolerances are different for outdoor and indoor networks, as the priorities are different. In the first case, to put it simply, the sewer should not be heard, and without the appearance of unpleasant odors. For outdoor in priority uninterrupted work that does not require constant monitoring and cleaning.

Slope depending on the diameter

The speed of the flow of effluents and the fullness of the pipe are important so that they flow freely into the collector or septic tank. However, both of these moments depend on the size of the pipe itself and the volume of effluents, and the diameter is selected based on the average daily volume of effluents and filling the pipes by 50-60%, but not less than a third at a speed of 0.7 m / s.

Any calculations come down to choosing one of the standard sizes: 50, 80, 100, 150, 200 mm. In practice, it remains only to clarify the slope for each size and the limits of permissible error.

The slope is defined in SNiP as a fractional coefficient. The value is determined by the ratio of the length to the required distance between the top and bottom points at the edges. The coefficient is numerically equal to the difference in height between the edges of a pipe one meter long, expressed in meters.

To get a bias sewer pipe one diameter on a flat area, it is necessary to multiply the length by the slope coefficient. If the result is multiplied by an additional 100, the value will be in centimeters.

Why is the tilt angle for different diameters is different? To comply with the requirement for the flow rate of effluents.

In a pipe with a diameter of 50 mm, the volume is much smaller, if only fullness is taken into account, but the contact of water with the surface increases, in comparison with 150 and 200 mm. A pipe with a smaller cross section is set at a large angle so that the water descends through it at the required speed and takes solid inclusions with it.

However, this only applies general requirements to the formation of internal and external sewerage and slope on even extended sections in the absence of a direct connection to siphons, outlet pipes, etc. For fittings and connection points used whole line rules.

internal

Slope for pipes:

• D 40 mm - 0.035;
• D 50 mm - 0.03;
• D 80 mm - 0.2;
• D 100 mm - 0.015.

In internal sewerage pipes with a diameter of 40, 50, 80 mm are used, and a diameter of 100 mm is used for common area at the connection point where the lines converge.

Adapters from one diameter to another are mounted so as to make a straight line along the lowest part, creating a continuous channel for draining. Slopes along different sides from the adapter are set according to their coefficient value.

The required slope is formed due to the fasteners on which the pipe rests, or due to the inclination of the strobe or box in which the sewer will be sewn up.

Area up to 1.5 meters from sink drain or connection household appliances can be laid in an arbitrary way while maintaining the obligatory slope from the drain to the sewer pipe.

The turn to the line of the sewer pipe is necessarily formed by an elbow or a tee with a slope of 67 degrees. The slope of the bend or the top of the elbow is oriented along the route towards the riser.

The connection to the riser must be formed by a cross or a tee with an outlet slope of 67 (87) degrees. It is advisable to replace rectangular tees, which can still be found in apartment buildings when replacing internal sewerage.

The scheme of the slope of tees and sewer turns

Outdoor

Slope for pipes:

• D 100 mm - 0.012;
• D 150 mm - 0.01;
• D 200 mm - 0.07.

The line of external sewerage from the house to the point of discharge must be in the same plane and with the same slope along the entire length. A combination of several pipe diameters or transitions in the line slope is not allowed. If for some reason you need to deviate from this rule, then at the articulation point various sites manhole is formed.

To form the required angle of descent, it is desirable to dig the trench itself, taking into account the increase in depth. Be sure to select the soil 20-25 cm deeper than the required sewer for the formation sand cushion. After that, part of the sand is poured, and supports are formed under each individual element. Next, the rest of the sand is poured with tamping.

How to set the angle of the pipe

The easiest way- usage bubble level with additional risks. If the flask with the bubble has three lines on each side, then this level is just right. Each line corresponds to a slope of 1 cm per meter.

The tool is fixed on top of the pipe, and then with the help of linings, a slope is set so that the bubble touches the desired mark.

Second way is a measurement of the distance from horizontal plane ends of the section. The ratio of the length of the pipe and the lift height of the upper side corresponds to the required slope factor.

Third way this is the leveling of two marks along the edges of the route. A thread or twine is stretched between them, along which they are already guided when compiling the pipeline.

The most obvious way- use a laser level and laser level to build the required plane. This will especially help when laying pipes in a strobe and sewing into walls using a box.

The entire sewage disposal system, mainly in private buildings, is based on the principle of water flow in a natural way, that is, by gravity. For the normal operation of this system, there must be a certain slope of the sewer. This means that the pipes do not have to be horizontal, but rather a slight slope is required so that the water flows under the force of gravity and does not stagnate in the pipes.

If the slope of the pipeline is too low, then the waste water will not flow out completely, as a result, blockages and plugs are possible. If the pipes are tilted too much, solid fractions of sewage can settle on their walls, which will also lead to the formation of plugs and wear of the pipes.

Therefore, there is a concept minimum slope sewerage, which guarantees a normal flow of water. There are special formulas for calculating this value, however, it is known from practice that that the slope should be approximately two centimeters per linear meter of pipe. This means that each meter of the subsequent pipe must be two centimeters lower. It is not difficult to calculate and make the required level of pipe inclination. Consider small example: the length of the drain pipe is 10 meters, which means that the horizontal distance between the beginning and end of the pipe will be twenty centimeters.

However, this takes into account only relatively pure water. And in the drains there are a lot of solid fecal fractions and fat, which solidify at a certain temperature and can accumulate on the walls of pipes. This can cause the sewer system to become clogged frequently and need to be cleaned periodically.

Therefore, SNiP (building norms and rules) determines the procedure for the construction of sewer systems. SNiP sewer pipe slope is taken into account already at the design stage of a private house or any other structure.

In accordance with these rules, pipelines with a diameter of up to 50 millimeters must have a slope of three centimeters per meter of pipe, and with a pipe cross section of up to 100 millimeters, this figure is already two centimeters.

The slope of the SNiP sewer pipe is taken into account only in centimeters, and this value is never measured in degrees. Experts do not determine the slope drain pipes in degrees, because even with a minimal error, the pipeline can be laid incorrectly. And this will lead to an unbalanced operation of the sewer system, there will be congestion, traffic jams and pipe cleaning will be required.

The slope of the pipelines of the internal sewerage system

Some advice from experts when installing internal sewerage:

• pipe turns at right angles in their horizontal position are not allowed, bends with an angle of 45 degrees should be used;
• with a vertical arrangement of pipes, right angles are permissible;
• in the places where the pipes turn, revision connections should be made to control and repair the system;
• at a short distance with a short pipe length, the slope can be made large (more than the permissible norm).

It should be noted that the SNiP slope of the sewer within the site prohibits changing the types of wiring. Otherwise, the hydrodynamic characteristics of the pipeline will be violated, which can lead to water hammer and, as a result, failure of the pipes. If any obstacle arises during the laying of pipes, then it is better to bypass it.

Calculation of the sewer slope when installing an external system

External sewerage is designed to deliver wastewater from the house to the septic tank. Pipes for this you can use various:

• cast iron,
• asbestos-cement,
• corrugated polyethylene elements.

The depth of the trench, depending on the climatic conditions of the region, can range from 70 centimeters to two meters.

The bottom of the trench should be approximately 20 centimeters deeper than the planned level.

This value depends on the diameter of the pipe, and it may also be necessary to add backfill to equalize the level of passage of the pipes.

In order to make the correct slope of the sewer, it is necessary to drive in two pegs at the beginning and end of the trench and pull the rope. In this case, the bottom of the trench can be made even, without holes and deflections, and the optimum angle of inclination of the pipes can be set. Then, at the bottom of the ditch, it is necessary to make a pillow of sand about five centimeters thick so that the pipeline lies flat and there are no hard protrusions that can damage the pipeline.

When building a system for the removal of wastewater and waste, the slope of the pipes plays an important role. It is important to comply with the sewer slope standards for the normal and trouble-free operation of the entire system. Depending on the length of the pipeline, the diameter and material of the pipes, the slope should be from 1.5 to 3 centimeters per linear meter of the pipe. These values ​​are checked by time and practice of specialists.

The sewerage system is divided into two parts: internal and external. The internal system consists of outlets (from bathrooms, showers, sinks, toilets), a riser and an outlet from the house. External system - from the pipeline and storage tank or septic tank. The internal pipeline, in turn, can be divided into vertical (risers) and horizontal (branches).

Sewer pipes

The vertical part requires ventilation and protection against clogging. Horizontal sections are called so conditionally, since in practice they are mounted at a certain angle with respect to the horizontal surface.

The rate of slope of sewer pipes - snip 2.0401-85. This document also defines the conditions for installing the system from the exit from the house to the first well, which must be located at least 12 m.

Sewer pipe slope calculation: basic concepts

If the sewer is gravity-flowing, then its efficiency in transporting wastewater due to the laws of gravity depends entirely on the angle of inclination. It is believed that wastewater should move through the pipeline at a speed of 0.7-1 m/s. Only in this case the flow is able to remove solid particles from the system. To keep the flow rate indicator, for each individual diameter, it is required to calculate the slope angle of the sewer pipe.

At first glance, it may seem that the angle should be measured in degrees. But in building codes and reference books on sewerage, this parameter is defined as a decimal fraction. These figures represent the ratio of level reduction to length. a certain area pipeline.

For example, on a pipeline section 5 m long, one end is 30 cm lower than the other. In this case, the slope of the sewer pipe will be 0.30/5=0.06.

Formula - determining the maximum, minimum value

The formula for calculating the slope of the sewer pipe

wherein:

• V speed of fluid flow (m/s);
• H filling pipeline;
• d pipe diameter;
• TO design factor tilt.

To determine the coefficient (slope), you can substitute V \u003d 0.7-1, d is the value of the diameter of a particular section of the pipeline, H \u003d 0.6xd (according to building codes and rules). It turns out that for a pipeline with a diameter of 100 mm per meter, a slope of 2 cm is required, with a diameter of 50 mm - 3 cm per meter.

It can be seen from the formula that the wastewater flow rate directly depends on the angle of inclination (coefficient). For optimal speed, a minimum sewer pipe slope of 0.02 and a maximum of 0.03 is required. If the roll is less than 0.02, large particles will settle and form a blockage.

If the bank is too large, the speed will increase, which will also lead to the formation of precipitation, since the water will leave too quickly, not having time to carry away the heavy particles of effluent. Increasing the flow rate can also lead to disruption of siphons and constipation.

Required standards in the apartment

When constructing a sewer, there is no need to use a formula for calculations. There is a table that defines the slopes for all taps from plumbing fixtures.

The optimal slope of the sewer pipes in the apartment
device	Drain diameter (mm)	Distance to siphon (cm)	Incline
Bath	40	100-130	0.033
Shower	40	150-170	0,029
Toilet	100	no more than 600	0,05
Sink	40	Up to 80	0,08
Bidet	30-40	70-100	0,05
Washing	30-40	130-150	0,02
Combined drain for bath, sink and shower	50	170-230	0,029
Riser	100
Withdrawal from the riser	65-754

Each section of the sewerage system in the apartment must have a siphon in the form of a device or a bend at the end so that unpleasant odors. To determine the required values, the principle of the golden mean is important - 1.5-2.5 cm per meter. This is quite enough for an apartment or country house. The use of formulas is necessary during construction large objects with the maximum volume of wastewater.

In addition, for domestic sewage, the formula is difficult to use, since there is no constant flow. Here it is better to pay attention to another indicator - the ability to self-clean (remove solid particles).

Since domestic wastewater contains waste with different weights, for heavy components the flow rate is the determining factor, for floating ones it is the filling of the system diameter. When determining the correct slope, it should be borne in mind that it will be different in each individual section.

The slope of the outer and inner parts of the system

In private country house it is necessary to arrange not only internal, but also external sewage. In addition, we need outlets for water, which is formed as a result of melting snow and precipitation in the form of rain. Storm sewer can be mounted together with the main system or separately.

The slope of the internal sewer pipe is strikingly different from that outdoor system. Tubular products are required for storm drainage large diameter(from 100 mm) and gratings, as this system will certainly get various pollution vegetable origin. The slope of the sewer for storm water should also be greater - 0.05-0.07, but not more than 0.15.

External waste from the house is usually directed to the central sewer or septic tank and is laid underground. The diameter of this pipeline is most often 100-150 mm. The minimum slope is 0.02. Based on this, a trench should be dug. If at earthworks inaccuracies were made, you can correct the situation with a sand cushion.

Any sewer must provide drains unobstructed flow and guarantee high level self-purification. It should certainly be borne in mind that the standards and textbooks indicate averages, so it never hurts common sense and practicality.

Over the years of designing water supply and sewerage networks, you communicate with many people: with customers, architects, designers, installers, designers of other sections. And the most frequently asked professional question sounds like this:

- With what slope should the sewerage be laid?
Of course, the answer to this question must be justified. Well, it is best to look for the basis in normative documentation. Inside buildings, pipes of small diameters are almost always used; we will use SNiP for internal networks.
Clause 18.2 of SNiP 2.04.01-85 * "Internal water supply and sewerage of buildings" says:

"... non-calculated sections of pipelines with a diameter of 40-50 mm should be laid with a slope of 0.03, and with a diameter of 85 and 100 mm - with a slope of 0.02."

For external sewerage, larger pipe diameters are used and they have their own standards. Paragraph 2.41 of SNiP 2.04.03-85 “Sewerage. External networks and structures" says the following:

"The smallest slopes of pipelines for all sewerage systems should be taken for pipes with diameters: 150 mm - 0.008, 200 mm - 0.007."

Well, clearly:

Usually, after silently listening to lines from SNiP on the phone, installers ask the second most frequent question:

- Well, if you really need to make the slope less?
Well, in SNiP there are several reservations on this topic. Regarding internal plumbing we are talking about "unaccounted sections" of pipelines. In the same paragraph 18.2 of SNiP 2.04.01-85 * there is a formula:

“Calculation of sewer pipelines should be made by assigning the speed of fluid movement V, m/s, and filling H/d in such a way that the condition

here K = 0.5 - for pipelines made of plastic and glass pipes;

TO= 0.6 - for pipelines made of other materials

At the same time, the velocity of the liquid must be at least 0.7 m / s, and the filling of the pipelines must be at least 0.3. "That is, theoretically, if you calculate the flow rate of effluents, then filling and, by checking the speed of effluents, you can get some other result.
You can also use the fundamental work of Lukinykh A.A. and Lukinykh N.A. “Tables for the hydraulic calculation of sewer pipelines and siphons according to the formula of A.A. Pavlovsky". By the way, these tables are also suitable for external sewer networks with their large diameters.
However, for pipes 150-200 mm for external sewerage networks in SNiP 2.04.03-85 there is a direct clause:

"Depending on local conditions, with appropriate justification for individual sections of the network, it is allowed to accept slopes for pipes with diameters: 200 mm - 0.005, 150 mm - 0.007."

That is, having the justification “very necessary” and great desire, you can save as much as 2 millimeters of slope per meter for pipes with a diameter of 200 mm.
Do not forget that, in addition to the minimum slope, there is also a maximum slope for laying sewer pipes. According to clause 18.3 of SNiP 2.04.01-85*

"The largest slope of pipelines should not exceed 0.15 (with the exception of branches from devices up to 1.5 m long)".

That is, a slope of 15 centimeters per meter. If this angle is exceeded during laying, then silting of the sewer pipeline is possible. Or, more simply, the water will quickly leave, and everything else will remain.
Keep the rules, Lord.

More useful information:

It’s impossible to lay pipes according to the “how it goes” principle, because most houses have a gravity drain system. It is capricious: if the slope is insufficient, then the sewer pipes will soon be clogged. And too much sewer slope of 1 meter will increase noise and cause leaks. These problems will entail the need to clean the system, which can be problematic.

Due to the fact that waste water may contain fats, food residues and debris, plaque forms on the inner surface of the pipes, it grows over time. Therefore, the angle of inclination is indicated in centimeters, and not in degrees, as is customary in ordinary life. If you also decide to start arranging the sewerage system, you should familiarize yourself with the standards and features of the calculation.

Determining the slope value

The slope of the external sewer in reference books and other specialized literature has the form of a decimal fraction. The ratio of the height of the decline to the length of the drainage system is indicated by the numbers 0.07 and 0.003. These data can be easily converted into units of measurement. In this case, we are talking about 7 cm or 3 mm per meter.

In order to determine the slope of the sewer by 1 meter, it is necessary to multiply the slope by the length of the pipe. As an example, consider a specific case where the length of the pipe will be 5600 mm, and the slope will be 0.07. To determine the slope of the sewer pipe, these two values ​​\u200b\u200bare multiplied, as a result, it will be possible to obtain 392 mm. The most suitable height difference between the end and the beginning of the drainage system will be a value of 39.2 cm.

The main parameters in determining the slope are the length and diameter. But in the design process, many forget that it is necessary to take into account the joints of the drainage system and the number of turns. It is recommended to take into account the number of discharge points and the features of drains. For the washbasin and toilet, they will be different. The slope of the sewerage by 1 meter depends on the diameter of the drainage system. If this value is 50 mm, then one side of the pipe must be lowered by 30 mm per meter.

For an 11 cm pipe, the slope will be 20 mm per meter. With a diameter of 16 cm, the minimum slope will be 0.008 m, which is equal to 8 mm. The calculation can also be carried out for pipes of impressive diameters. This parameter can be 200 mm. In this case, the pipe inclines at each meter by 7 mm.

Slope for internal piping

After studying the sanitary norms and rules, you can understand that the slope of the pipe will depend on its diameter. This should be understood as communications in the apartment. Bathrooms and kitchens use different products, so there are normal and minimum values. Within these limits, you should work. For kitchen sink and sinks, bathtubs, urinals and washbasins, pipes with a diameter of 40 or 50 mm are usually used. For them, the normal slope is 0.035. As for the minimum value, it is equal to 0.025.

The minimum slope of the sewer must also be taken into account when installing the toilet. A 100 mm pipe is used for the branch line. The minimum slope in this case is 0.012, while the normal one is 0.02. To determine the angle of inclination, it is recommended to use a bubble or laser level. The standard of horizontality should not be considered the floor. It is cheaper to purchase a special tool than to redo the sewer system afterward or repair yourself or your neighbors.

Sanitary norms and rules for external sewer pipes

By looking at the building codes (2.04.03-85), you can find out what are optimal dimensions slope for external pipes. Their diameter will be larger compared to the internal drainage. It is impossible to significantly exceed the recommended values, otherwise the sewage system will not work properly, the pipes will silt up and quickly clog. The maximum sewer slope for a 150 mm pipe is 0.008 m or 0.8 cm per meter of length. If the pipeline has a diameter of 200 mm, then this value will be less, it will be 0.7 cm or 0.007 m.

Conditions may arise when it is not possible to create a normal slope. In this case, the minimum values ​​should be used. For the first case, they are equal to 0.007 m or 0.7 cm. If we are talking about a 200 mm pipe, then they are equal to 0.005 m or 0.5 cm. For each meter, the maximum allowable slope is 15 cm or 0.15 mm.

Sanitary norms and rules for the fullness of sewer pipes

The sewerage system must be equipped in accordance with the rules that determine the fullness of the pipes. To calculate, use the formula K = H / D, in which the letter K means the fullness of the pipe. The letter H determines the height of the level of drains. The diameter of the sewer pipe is D.

The indicator of fullness is equivalent to one if the pipe is filled. For an empty drainage system, the value of K is understood to be zero. Optimal value is in the range from 0.5 to 0.6. This is true if the system is operating normally. The value may vary within these limits, which will depend on the materials in the basis of the products. They differ in the ability to form a boundary layer.

For ceramic or asbestos-cement pipes, the fullness index is 0.6. They are characterized by roughness, which cannot be said about plastic products. The recommended fullness for the latter is 0.5. If these values ​​are met, then the wastewater will pass at a speed equal to 0.7 m/s. This is enough to keep the solid particles in suspension and not settle or stick to the walls.

About sewers

The sewer riser must also be mounted taking into account sanitary norms and rules. When the element moves from a vertical position to a horizontal pipeline, it is not allowed to use a 90 ° bend. The following variations can be applied:

• three 30° elbows;
• two 45° elbows;
• four elbows of 22.5° each.

In each case, the angle of inclination of the system from the riser to the horizontal pipe must be carried out by more than one transition. If this rule is observed, then it will be possible to reduce the turbulence of the flow and eliminate frequent blockages. The sewer riser is equipped according to a different principle, if the wiring is carried out using several plumbing fixtures, the number of which sometimes reaches six.

Sewerage scheme of a private house

Sewerage in a private house, the scheme of which will be described below, should be equipped in accordance with SNiP. Concerning internal system, then its main riser should be installed closer to the wall through which the sewer is brought out. This wall should be located as close as possible to sewer well, which is located at the lowest point of the site.

The sewerage system provides for a vertical joint, which is usually represented by a 110 mm pipe. Pipes are connected to it, which are connected to plumbing fixtures. For a toilet, these are usually straight sections using 100 mm pipes. There is another scheme that provides for the arrangement of sections with tees, bends and crosses, the diameter can vary from 32 to 80 mm.

As for the external sewerage, it must be connected to inner pipes no bends or bends. It is better to use plastic products. They are located taking into account the level of freezing of the soil. The pipeline is laid below this line so that the products do not freeze during frost. External sewerage provides for the presence of a well, the volume of which is calculated taking into account the drains.

Sanitary norms and rules

When arranging the described system, SNiP must be used. Sewerage inside at the same time implies the need for a water seal when installing plumbing fixtures. When laying internal networks, cast iron or polymer pipes. The diameter of the outlet from the house should not be less than 110 mm. Internal networks usually equipped with ventilation. Ventilation of networks is provided through the joints; for this, an exhaust part must be located above each of them.

If you decide to do the described work yourself, then you must be guided by SNiP. Sewerage outside must be laid using pipes with a diameter of 150 mm or more. In this case, the depth of the tray is 1.1 m. Wells must be provided for cleaning and maintaining networks. For gravity flow schemes, it is necessary to use asbestos-cement, polymer and ceramic pipes.

You can independently equip a sewerage system in a private house, the scheme of this system may suggest the presence of a treatment plant. She is an integral part autonomous sewerage. Among the main treatment facilities should be highlighted:

• storage septic tank;
• cleaning type septic tanks;
• stations for deep biological treatment or aeration tanks.

Conclusion

A sewer slope of 1 meter must be observed. This was discussed above. If the slope angle is made too large, then the gravity system will not be able to work correctly. Deposits of fats and other substances will occur on the walls of the pipes. If you make the slope too high, you will have a system that cannot function correctly. The liquid will effectively go outside, but the solids will remain inside.