Sewer Pipe Drop?

Question

What is the standard drop for sewer pipe? Example: I have 20 ft of 4" sewer pipe, what would be the drop per foot (max/min) from the home to the main? Is there a formula for this?

Answer 1

to meet code, a sewer should have one quarter inch slope per foot, so if you have a run of 20 feet, you would need a drop of four inches.

I assume you live in the USA, but sometimes it is wrong to assume.

Basically if the slope was too much, the water would drain too quickly leaving solids behind, if the slope was not enough, the flow would be too slow, therefore it could cause a blockage.

I hope this informstion shall be of benefit to you, and good luck with the project.

Paul

Answer 2

Try to get as close as you can to 1/4 " per foot  but the least you can have is 1/8'' per foot . Your situation is different because from the house to the main sewer is a fixed distanceand depth ...Soo .... install it  as stright and on grade as you can safely do.  DO NOT GET INTO A UN SHORED TRENCH OVER FIVE FEET DEEP!!!! and  dont forget a cleanout at the house side. Proper venting of the inside plumbing will prevent "siphoning of the traps"so that not the problem with too much fall the problem is the liquid waste flows faster than the solid waste leaveing it in the pipe and potentialy creating a " log-jam" (pardon the visual.).... any way if its in the main and sombody showers, or does dishes, or brushes their teeth (only liquids draining) at least once a day you most likely will not have a problem even at 4" per foot of fall but for short runs only!!  less than 8'

Answer 3

1/4"per foot is the minimum required by most codes up to 6" pipe.

With plastic, you can not have to much slope. That's old knowledge that pertained to clay tile systems. Give plastic as much slope as you want, but no less than 1/4" per foot.

In your example, a 20 foot joint of pipe would have 5 inches of drop minimum.

Answer 4

Minimum of 1/4 inch per foot is ideal, maximum of 1/2 inch per foot for shorter runs..

Any more pitch will start to siphon the traps.