I've heard 1/4" per foot and I've also heard 1/8" per foot is acceptable for waste lines. What is the ideal slope? Does it depend on pipe size or fixture type? (i.e. toilet vs sink)

Thanks!

RickJ

We've always used 1/4" and I've heard from many that this is the standard. I've never heard of 1/8" per foot.

I'd consider going 1/8" per foot if it were a sink or other liquid only drain, but certainly not for a toilet.

mwarney

Thanks for clearing that up. I'm not sure where I read it but somewhere I remember instructions to maintain between 1/8" and 1/4" per foot. A plumber once told me to have "Half a bubble" on the level.

RickJ

I'd far more trust a ruler than a level for something as important as slope. You sure don't want to be re-doing it later.

allozier

I usually use 1/4 in per foot which equals about a quarter bubble on a nine inch torpedo level. but with these 1.6 flush toilets they sell these days I have found that 1/4 in tends to let the water go by and hold the waste back and eventually build up and stop up. So I tend to run a little less slope on lines with toilets on them. You might check wih other plumbers to see what they think but it works for me.

speedball1

When we rough in for drainage we just crack the bubble on a level. In all the hundreds of rough ins we have done in my area we have never had a problem using this method. Only once, when I put in a super market was I held to using a transit on the refrigeration drains. I consider half a bubble to be too much fall. Regards, Tom

mwarney

Thanks Tom, Any idea what that interprets to (in terms of slope per foot)?

speedball1

"Any idea what that interprets to (in terms of slope per foot)?"

I never really figured it out mathematically but my guess would be 1/8th inch to the foot. cheers, Tom

speedball1

Sounds complicated to me Rick,
Would you explain how that goes for the rest of us. The only time I've ever used a ruler is when I was held to zero slope putting in super market reefer lines and had to use a transit to do it. Regards, Tom

massplumber2008

By the way Mwarney...

Plumbing codes in the USA mandate that pipes 3" and smaller get 1/4" pitch per foot minimum.

Pipes 4" and larger can have a minimum 1/8" pitch per foot.

If not on commercial job using a transit level to keep track of slope I take a 4 foot level and I tape a 1/2" block of wood at the very end of the level which is equal to 1/8" pitch per foot so that when I place the level on the 4" or 6" underground pipe, for example, and get a level reading from the level I know I have a properly pitched pipe for sure!

Good luck!

MARK