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

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by dohc, Jun 14, 2019.

  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".
     
  3. Sponsor

    Sponsor Paid Advertisement

     
  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
  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 4”, except as a building drain. Using 3” allows the pipe to be scoured properly, which reduces clogging.

    A toilet can be wet vented through the lavatory vent, by connecting the 2” drain downstream of the closet bend.
     
  7. dohc

    dohc New Member

    Joined:
    Oct 31, 2018
    Location:
    Wisconsin
    Reach4, interesting that you suggested the 4 x 3. After looking closer, I think the code requries a 4" closet flange...

    (c) Water closets. A water closet shall discharge through a drain pipe or fitting with a minimum diameter of 3".
    2. A floor outlet water closet shall connect to a 4 inch or 4 × 3 inch closet collar fitting. A 4 ×3 inch closet bend fitting may be installed where a 4 inch closet collar fitting is used.

    Do they even make a 3" closet flange?
     
  8. Reach4

    Reach4 Well-Known Member

    Joined:
    Sep 25, 2013
    Location:
    IL
    Yes. Lots of them.

    Possibly the most common is a "4 in. x 3 in. " Closet Flange. It glues either outside of a 3 inch pipe or inside a 4 inch pipe.

    There are 3-inch inside. 3-inch outside. The 3-inch inside are often avoided because they have the narrowest passage, although that passage is still bigger than the output of a toilet. There are all kinds of variations.

    A 4 inch pipe or closet bend has the advantage that both the inside and outside can be used over time, which can come in handy during rework/remodel.

    Some flanges use compression rather than glue. Those would seem to be an advantage to those who are less practiced and might be concerned about the need to get it right the first time with glue. I am not a plumber.

    Stainless steel rings on the closet flange are more sturdy than plastic. They are more rust-resistant than painted steel, although the painted steel should be good for decades.
     
  9. hj

    hj Moderator & Master Plumber Staff Member

    Joined:
    Aug 31, 2004
    Occupation:
    Plumber
    Location:
    Cave Creek, Arizona
    Whether you use 3" or 4", the "number" of parts is the same, if it is done properly.
     
Similar Threads: Water Closet
Forum Title Date
Plumbing Forum, Professional & DIY Advice Water Closet Directly Over Stack Mar 15, 2019
Plumbing Forum, Professional & DIY Advice Water Closet Venting Aug 23, 2018
Plumbing Forum, Professional & DIY Advice Air Admittance Valve in water closet Jun 20, 2018
Plumbing Forum, Professional & DIY Advice Horizontal wet vent discharge into vertical water closet segment Jan 29, 2018
Plumbing Forum, Professional & DIY Advice Vent below a water closet? Jan 4, 2016

Share This Page