Very Novice Do It Yourself'er, Installing Comode 20' from line in basement. Already jackhammered concrete. What slope should I use on the line going from the new lav to the main. My thoughts are about 2.75 inches down for every three inches of pipe. I'd like to go less but I'm not sure if that would be safe.

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Originally Posted by Dan S

Very Novice Do It Yourself'er, Installing Comode 20' from line in basement. Already jackhammered concrete. What slope should I use on the line going from the new lav to the main. My thoughts are about 2.75 inches down for every three inches of pipe. I'd like to go less but I'm not sure if that would be safe.

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Hi Dan,
I'm going to post a answer I gave yesterday before I address your concerns.

" Let me tell you how a typical basement bathroom group rough in goes down.
4" under the cement from the toilet to the main sewer. 2" from the lavatory to connect to the 4" toilet drain line. From the top of the lavatory stubout tee a vent line will be run through the roof or revented back to a existing dry vent line in the attic. 2" from the shower to connect to the lav drain where it will be wet vented as will the toilet."

Now for your question.
The normal slope for drainage should be 1/4" to the foot. Although, if height is a problem 1/8th is acceptable. Too little slope and the discharge will not drain. Too much slope and the water will rush by so fast that the solids will be left behind to clog up. Your slope of 2 3/4" every 3" works out to 11" per foot. A almost vertical fall.

Dan, 2 3/4" per every 3 feet is still too much fall. For 3' you should have 3/4" of slope. Regards, Tom