1/4” per foot (2%) minimum for drain pipes that will contain sewage.
Pitch on a sewer line for a building or home
In the cases of a 6″ sewer line the minimum recommended pitch on a sewer line is 1/4″ per foot, or about one foot for a fifty-foot run.
The maximum fall for a waste pipe is 1 in 40. The minimum fall is 1 in 110 (apart from vertical pipes, but that's a different story). So pipes with a gradient between 1 in 40 and 1 in 110 should have adequate flow to prevent blockages from occurring.
Pipes must slope slightly downhill to drain properly. The standard slope is anywhere from ¼ inch to 3 inches per foot depending on the use. An accurate calculation is essential for properly functioning plumbing.
The most important bit of obvious advice ever: soil and waste pipes need to be on a downhill gradient! The “fall” or “drop” should be between 1/40 (1cm down for every 40cm across) and 1/110.
The maximum longitudinal grade along the easement shall be 8%. The maximum cross slope within easement boundaries shall be 4%.
The ideal slope of any drain line is ¼ inch per foot of pipe. In other words, for every foot the pipe travels horizontally, it should be dropping ¼ inch vertically. Many drains either have too little slope or too much slope. That's right, it is possible to have too much slope in your drain lines.
a 1 in 40 drop is 25mm drop in a 1 metre run. To measure that, I have a standard 1 metre long level, and I tape a small bit of 2*1 timber to one end of the level, then set the pipe so the level reads level and you have a 1 in 40 fall.
A gradient of 1:60 means that there will be 1 unit of fall for every 60 units of patio width. The patio is to be 4.2m wide, so if that distance (the run) is divided by 60, the result is the 1 unit of fall. We'll work in millimetres rather than metres... From the above.... Fall = 4,200mm ÷ 60 = 70mm.
A 4-inch horizontal drainage pipe's minimum slope is 1% to 2% (or 1/8 inch to 1/4 inch per foot). The pipe should slope downward 1/8 inch to 1/4 inch per foot for drainage and to prevent clogs.
If the underground sewer pipe is to stay below ground it must follow the average gradient of the slope. This invariably means that the pipe gradient becomes too steep, resulting in the solids being left stranded in the pipe causing a blockage.
Using a minimum slope of 2% will encourage a good flow when directing water to a rain garden. For a 2% slope your pipe height will lower ~¼ inch for every foot of length. You can also approximate this by multiplying the pipe length in inches by . 02.
In a conventional gravity system, the pipe from the house to the septic tank, and the outlet pipe from the tank to the distribution box or leach field, should both slope downward with a minimum slope of 1/4 in. per ft. (1/8 in. per ft.
Re: Are 45 degree fittings allowed in horizontal drain pipe? To answer your question, yes they are allowed, but only in a horizontal configuration. You cannot use them to change elevation.
The maximum fall for a waste pipe is 1 in 40. The minimum fall is 1 in 110 (apart from vertical pipes, but that's a different story). So pipes with a gradient between 1 in 40 and 1 in 110 should have adequate flow to prevent blockages from occurring.
Recommended Slope for Toilet Drain Pipes
The universally accepted standard for a toilet drain pipe slope is a quarter inch per foot of pipe (1/4 inch per foot). This means for every foot the pipe travels horizontally, it should drop in elevation by one quarter of an inch to facilitate proper flow.
If it's too steep, water and solids can separate, causing solids to accumulate in the pipe.
For instance, residential sewer line depth ranges from 18 to 30 inches. However, city sewer line depths are different. Your city's sewer lines must always be deeper than the deepest residential pipe to allow waste to flow downhill. As such, these lines can go as deep as needed.
Maximum grade is generally 15% for 8" and decreases to 4% for a 24".
4″ waste line can support 90 DFU's, Toilets can be 3–4 DFU's depending on how many gallons per flush. So, 22 toilets if they use a lot of water.
Two-percent slope is required for 21/2-inch (64 mm) diameter and smaller pipe, and 1-percent slope is required for 3-inch (76 mm) diameter and larger pipe.