Hi: I am building a new home. Due to my existing home problems with sewer drain clogs, I am concerned that my new home will have same issues. Plumbers install rough-in pipes today. I used a level and noticed several sections of the pipe were level and did not show a drop. What is the recommended drop in line to insure ideal drain of toilets? Does the drop need to be at all lengths or can there be perfectly level drain sections?

Drain lines are normally sloped 1/4 inch per foot of horizontal run but sometimes it will be done a little more or less than that under certain conditions. I don't think the pipe should ever be level or back-sloped. Be careful about sloping the pipe too much, that will aid the water to run off too quickly and possibly leave solid matter behind in the pipe. The water needs to move slowly enough to carry solid waste with it.

Why not discuss your concerns with the plumber doing the work or with the contractor building the home?



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It is an "old wive's tale" that too much slope is bad. After all, vertical pipes have "infinite slope".

And solid waste drops straight down on vertical pipes, so the slope in a vertical pipe is not a consideration. It is the horizontal runs that are the worry. How do you slope the drain lines you install?



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I use whatever grade is available, point A to point B. Universitylaboratory tests have shown that the AMOUNT of grade is irrelevant as long as it is not flat.



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So the misunderstanding is that a slope of 1/4 inch per foot is actually the minimum slope, to ensure it isn't flat, and a greater slope is just fine?



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absolutely wrong... the pipe must be removed and re-installed with the proper slope.
best way to check for slope is.... get a 4 foot level and glue a 1 inch block on one end. set the level on the pipe and it should read level..

That's the way I have always done it.

Wow, I have read seven replies. Good ideas and thoughts. Obvious, there are some different opinions out there. Based on the replies, I;m going with a four foot level and a 1 inch block...I did this and found a few locations "level" or "flat", most were 1/4" sloped. No back sloped, thankfully. Yes, I will go to my contractor, but needed to know the answer before I asked the question! Once slap is poured, it is impossible to get anyone to accept responsibility for resulting problems.
Thank you all.



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Here in NC under UPC code 3" and 4" pipe can be sloped at 1/8" per foot. 2" and smaller must be sloped at least 1/4".

I was under the impression that a slope much greater than a 1/4 in per foot (like 1 in per foot) results in liquids outrunning the solids and possibly leaving some solids behind.

Vertical pipes (45 deg or greater) are different in that the solids will move by themselves.

I agree with HJ that 'too much slope' is an old wives tale and makes no sense. I've installed drains at 45 degrees and never seen a problem. You see problems with not enough fall, but never with too much.