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Thread: Shower and Toilet Venting Question

  1. #1
    DIY Junior Member David1980's Avatar
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    Jan 2012

    Default Shower and Toilet Venting Question

    I have spent probably 6-8 hours reading through this forum and other sites in an effort to figure out the correct way to run the waste lines for a bathroom remodel. Hopefully, someone here can tell me if I have it right or not!

    Basically, I need to drain a new shower into an existing toilet waste. The toilet waste is 3" and then changes to a 2" vent running up to the roof. My first thought was to simply run a 2" drain for the shower into the 2" toilet vent, which is located above the toilet connection. It seems though that the correct way to do it might be to connect the shower drain below the spot where the toilet connects. I have attached two rough drawings. They are not to scale and do not show the fittings...I'm just trying to get an idea of how to do the layout. I appreciate any help!Name:  bathroom drain1.jpg
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Size:  11.8 KBName:  bathroom drain2.jpg
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  2. #2
    Forum Admin, Expert Plumber Terry's Avatar
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    Aug 2004
    Bothell, Washington
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    The trap arm on the shower needs to be nearly level before the vent.
    You are allowed 1/4" per foot grade, up to five feet before it's vented with the Uniform Plumbing Code, which is used in Oregon.
    Therefor, it would be the top drawing.

    A wet vent needs to be a minimum of 2", which you have now as the toilet vent.

  3. #3
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona


    The shower connection ABOVE the toilet is correct. Putting it below the toilet connection would require that you install a vent on the shower drain line.
    Licensed residential and commercial plumber

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