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.
In other words, for every 100 feet the pipe travels horizontally, it should drop about half a foot vertically. A pipe with a 30-inch diameter should have a minimum of 0.06 feet (less than three-fourths of an inch) in slope per 100 feet.
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.
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.
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.
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.
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. Too steep (1/10) then the water runs quicker than the solids so doesn't wash them away (ugh!).
The optimal slope for drain pipes typically ranges from 1/4 inch to 3 inches of fall per foot of length, depending on the pipe's diameter and the type of waste it carries. The larger the pipe, the less slope it requires to move wastewater effectively.
To calculate drainage fall, divide the total length by the fall ratio. For a 1 in 40 fall, divide the length of the pipe by 40.
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.
Drain pipes for sewage is supposed to be 1/4″ per foot (1″ per 4′, 2cm per meter).
The trench should be about 18 inches deep and 9 to 12 inches wide.
General. 1) Sewer lines shall be laid on a straight alignment and uniform slope between consecutive manholes. 2) Horizontal and vertical curves in sanitary sewers are not permitted.
Horizontal drainage piping of 3-inch diameter and less shall be installed with a fall of not less than 1/4 inch per foot. Horizontal drainage piping of more than 3 inches and up to and including 6 inches in diameter shall be installed with a fall not less than 1/8 inch per foot.
Vertical drops from fixture traps to horizontal branch piping shall be one size larger than the trap size, but not less than 2 inches (50 mm) in diameter. Vertical drops shall be 4 feet (1219 mm) maximum length.
2% is 1 in 50, so a 2% slope is roughly 1/4″ rise per foot.
A 3-inch sanitary waste line is sufficient for one bathroom group (toilet, lavatory, tub/shower) but a whole single-family house tends to have a 4-inch default size, at least entering the building.
Regardless of surface characteristics, when it comes to surface drainage, slope is the most important issue to consider. For efficient drainage, paved surfaces should have a minimum 1-percent slope. Turf or landscaped areas should have a minimum slope of 2 percent.
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.
1/4”/foot is correct and yes you can grade too much. Aim for 1/4”, anything more is too much, anything less not enough.
A gradient of 1 in 80 is suitable for commencing calculations for pipe schemes. If the gradient is less than 1 in 110, then the pipe could still block if the solids slow down and become stranded. If a 48 metre section of drainage pipe has a fall of 0.60 metres, the gradient would be calculated as follows.