4" or 3" Water Closet (Toilet) DW pipe

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dohc, Jun 14, 2019 at 9:16 AM.

  1. dohc

    dohc New Member

    Joined:
    Oct 31, 2018
    Location:
    Wisconsin
    Is there any reason I would NOT want to use 4" pipe all the way to the toilet flange. I could reduce it down to 3", but it is just as easy to keep it 4" and uses less fittings (no need for a 3" to 4" reducer). Is 4" ok?

    As for the vent, that is about 5' away and will be 3" to fit in the wall.

    4inch Toilet Pipe.png
     
  2. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    The toilet can be a 3" and the vent can be a 2"
    You can also do the whole thing in 4" if you want.

    I think 3" has better drain line carry for a single or double installation. Water kind of flattens out on 4".
     
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  4. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    If you use 3 inch pipe, you should consider a 4 x 3 closet bend at the toilet. There are various forms. The one pictured is the "spigot" type.
    [​IMG]

    If you have a lavatory as part of the install, that can often serve to vent the toilet too.
     
  5. dohc

    dohc New Member

    Joined:
    Oct 31, 2018
    Location:
    Wisconsin
    I will use 4" all the way to the closet flange then as it is less parts.

    Could a lavatory, using a 2" pipe running about 6', drain and direct vent into this 4" between the toilet and 3" vent?

    Thanks for all the help Sink Toilet.png
     
    Last edited: Jun 14, 2019 at 11:10 AM
  6. cacher_chick

    cacher_chick Test, Don't Guess!

    Joined:
    Jan 5, 2008
    Occupation:
    Test, Don't Guess!
    Location:
    Land of Cheese
    With the reduced water use fixtures of today, there is no reason to use 4โ€, except as a building drain. Using 3โ€ allows the pipe to be scoured properly, which reduces clogging.

    A toilet can be wet vented through the lavatory vent, by connecting the 2โ€ drain downstream of the closet bend.
     
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