Plumbing a new toilet - Is 3" Pipe Good Enough?


Old 03-30-08, 05:20 PM
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Plumbing a new toilet - Is 3" Pipe Good Enough?

I'm building a basement downstairs in my house and have plumbed in a new toilet, sink and bath. The main waste drain from the toilet is a 3" pipe, laid horizontally, that has one Y-connector. The main waste pipe for the house is a 4" cast iron.

The question is: is the 3" pipe OK for the toilet or should it be replaced with a 4" pipe?
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Old 03-30-08, 06:23 PM
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3" should be OK as long as it is sloped 1/8" per ft. to main
Old 04-01-08, 02:12 PM
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Check the code, if your waste drain is under concrete, I believe it is required to be 4" DWV pipe.
Old 04-03-08, 07:50 PM
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Do four...whats the cost difference? $10?
Old 04-03-08, 08:38 PM
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FWIW - My last 3 basement bathroom additions had 3 inch pipe - under concrete - and all three passed code (2 different states).. Using a 4 inch pipe certainly wouldn't hurt - but since the toilet drain opening is only 2inches +/- - I figure that three inch pipe isn't gonna have issues...
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