3" Sewer Pipe?

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Old 02-27-2007, 03:26 AM   #1
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3" Sewer Pipe?

Heired a plumber / freind to help me revamp a house.
Quotes me $ 3500 .00 for six fixtures & a new drain ( 12 foot run)
Good enough. Everybody has to make a living right?. Into the job he runs 3" drain through the existing cast iron to make it through the perimiter beam. All of the drain pipe is 3" after the log launcher.
#1 Will this work? The D pipe has about a 2" grade on the run.
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Old 02-27-2007, 07:59 AM   #2
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Re: 3" Sewer Pipe?

I'm not sure what a "D" pipe is, or what you mean by 2" grade. Two inchers per foot?

As for 3", this all depends on the fixtures upstream that the pipe services. Usually, this is OK for the first water closet, but has to go to 4" when the second water closet is added to the line, depending on the code in your area.

Three inch pipe can service quite a number of fixtures, but plumbers size pipes by fixture units, not just 'fixtures'. This is why I say it depends on the fixtures upstream of the 3".


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Old 02-27-2007, 08:45 AM   #3
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Re: 3" Sewer Pipe?

My take may be different but here's the way I see it.

3" up to 5 commodes, 4" for 6 or more. Though it's true that other fixtures produce waste, it's the commodes that produce a significant load in a short time.

Oversizing can be a problem. Pipes are self cleaning but an oversized pipe can leave waste at bends that doesn't self clean, adding up to later problems.

I was chastised by an inspector for oversizing the pipes on my own house 25 years ago. 4" with 6 commodes. He said, though it was code compliant, there would never be a time when all would flush simultaneously so the pipes were functionally oversized and could be a problem later. In the subsequent years we haven't had any problems.
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Old 02-27-2007, 06:30 PM   #4
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Re: 3" Sewer Pipe?

Sounds like I'm ok then. Thanks
One more about the ac drain if you don't mind. Which is the best way to run it? The over flow runs out through the soffit. The main is now run forward of a pee trap in a sink. To make that run the pipe is longer & has less grade than it would if it were run into the closest vent pipe. My plumber freind said doing that is not code & could allow sewer gas into the ac system.
What would you do? I'm not permiting this job.
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Old 02-27-2007, 06:41 PM   #5
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Re: 3" Sewer Pipe?

Originally Posted by elarofcrankcase View Post
What would you do? I'm not permiting this job.
I'd get a permit.
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Old 02-28-2007, 07:17 AM   #6
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Re: 3" Sewer Pipe?

Originally Posted by elarofcrankcase View Post
The D pipe has about a 2" grade on the run.
Run is 12' and that requires 3" of grade.

1/4" per foot, calculates out to be 8' run, what am I not seeing here? is it under-graded?

Last edited by Ron The Plumber; 02-28-2007 at 07:22 AM.
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Old 02-28-2007, 07:37 AM   #7
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Re: 3" Sewer Pipe?

What state are you in? In Florida 3" pipe gets 1/8" slope per foot and carries up to 20 fixture units.


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