Septic Main Sewer Line

[4570Man]

Main septic lines are usually required to have 1/8” - 1/4” fall per foot, not 10’.
1/8” - 1/4” fall per 10’ is usually for drainage tile (water).

That’s what I was thinking that 1/8 inch per stick of pipe wasn’t any fall at all.

 

[Pettrix]

Building department responded:

"The requirements for a sewer line that long are that it needs to meet the minimum slope and you will need a cleanout at the exit from the structure and every 100 in length of the line. Pipe Slope (min and max):3 pipe= ¼ per foot. 4 or greater pipe = ⅛ per foot."


On a 4" pipe:
So that would be 2.5 inches per 10' or 37.5 inches of slope for the 150'. (at 1/4" per foot)
So that would be 1.25 inches per 10' or 18.75 inches of slope for the 150' (at 1/8" per foot)

As long as I have 19" - 38" of drop from the house to the tank, I am good. I will go with the steeper drop.

 

[MossRoad]

I can't remember where I saw it, maybe ask this old house, a video of sewage drainage pipe made with clear plastic so you could see how too little, too much, and just right sloped pipe worked. It was pretty interesting and something your average do-it-yourselfer wouldn't think about.

Too little slope and the water doesn't push the solids down the pipe.
Too much slope and the water outruns the solids and doesn't wash them down the pipe.
Just right and the water moves the solids down the pipe just right.

The clear pipe really let you see how it worked. I wish I could find those videos again.

 

[Ford850]

Building department responded:

"The requirements for a sewer line that long are that it needs to meet the minimum slope and you will need a cleanout at the exit from the structure and every 100 in length of the line. Pipe Slope (min and max):3 pipe= ¼ per foot. 4 or greater pipe = ⅛ per foot."


On a 4" pipe:
So that would be 2.5 inches per 10' or 37.5 inches of slope for the 150'. (at 1/4" per foot)
So that would be 1.25 inches per 10' or 18.75 inches of slope for the 150' (at 1/8" per foot)

As long as I have 19" - 38" of drop from the house to the tank, I am good. I will go with the steeper drop.

It sounds like you're on the right track now. :thumbsup:

 

[Welshman]

I can't remember where I saw it, maybe ask this old house, a video of sewage drainage pipe made with clear plastic so you could see how too little, too much, and just right sloped pipe worked. It was pretty interesting and something your average do-it-yourselfer wouldn't think about.

Too little slope and the water doesn't push the solids down the pipe.
Too much slope and the water outruns the solids and doesn't wash them down the pipe.
Just right and the water moves the solids down the pipe just right.

The clear pipe really let you see how it worked. I wish I could find those videos again.

I remember seeing that too. It was on Ask This Old House.