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Thread: minimum drain pipe size for a lav

  1. #1
    DIY Junior Member poky1234's Avatar
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    Default minimum drain pipe size for a lav

    Hello, Can someone tell me if an 1 1/4 pipe can be used to drain a lav? The drain pipe would run 4 to 5 feet ,then connect into the vertical 3 inch main waste stack. Also , because of the short distance,would it still require its own vent?

    Thanks

  2. #2
    Test, Don't Guess! cacher_chick's Avatar
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    In the U.S., the trap and trap arm of a lav is commonly 1-1/4", but the drain is run in 1-1/2".

    From the International Plumbing Code (IPC)
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  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    The lav should have a vent before it enters any "waste" stack.

    A lav can wet vent a shower, tub or toilet, but you can not run down waste on top of it in that manner.
    Last edited by Terry; 04-01-2013 at 08:51 AM.

  4. #4

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    it can be 1-1/4" drain and can be stack vented if there is no discharge upstream of where it connects to the 3" main. If there is discharge from above that connection then it does require tis own separate vent

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    DIY Junior Member poky1234's Avatar
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    Quote Originally Posted by mikeplummer View Post
    it can be 1-1/4" drain and can be stack vented if there is no discharge upstream of where it connects to the 3" main. If there is discharge from above that connection then it does require tis own separate vent
    Thanks for the replies guys. Mikeplumber, that is exactly what we are doing. I just needed to know if 1 1/4 is ok. This is for a custom floating boathouse that has very tight quarters and is a little unconventional. I have another question but I'll post it with a pic and drawing.

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