toilet drain 3" or 4"?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by zxed, Feb 1, 2009.

  1. zxed

    zxed New Member

    Messages:
    61
    Location:
    California
    question about my toilet drain.... i want to know if there is any specific reason if the following is done (see image)

    i can guess that the 4" allows for a smoother flush...

    the current setup is for a 14" toilet rough, the new toilet is a 12"..

    since i need to move it back., should i simply move it 2 inches back, or should i re-create with a 3" drain and 4" to 3" flange?

    Attached Files:

  2. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    I'm not understanding your post.
    Are you planning on having a 4" line at the toilet that then goes into a 3" line further down?
  3. iminaquagmire

    iminaquagmire DIY Senior Member

    Messages:
    207
    Use a 3x4 reducing closet bend. It'll have a 4" inlet and a 3" outlet. Makes setting the flange much easier since you use a 4" inside fit flange. I would change it for that reason alone. That way you can leave the pipe long and tile up to it. Then when your floor is done, you can trim the pipe flush and install your flange on top of the tile for a perfect, fully supported flange. I wouldn't use any reducing couplings anywhere.
    Last edited: Feb 1, 2009
  4. zxed

    zxed New Member

    Messages:
    61
    Location:
    California
    i like the idea of triming the pipe flush after all the flooring is done..

    so something like this

    so once i attach the 3" to the horizontal waste drain, i will still need to drop in a 4" pipe for the top so that it sticks out high enough for me to cut flush later correct?
    Last edited: Feb 1, 2009
  5. zxed

    zxed New Member

    Messages:
    61
    Location:
    California
    that is what is there right now. i was asking if that is fine or if i should change it 3" all the way
  6. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    It should be 3" all the way!
  7. zxed

    zxed New Member

    Messages:
    61
    Location:
    California
    any clue why they (original home construction back in 1979) would install it the other way? 4" turning into a 3"
  8. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,831
    Location:
    Cave Creek, Arizona
    bend

    For the same reason I still only do it that way. It makes a better installation, but I use the 4x3 hub and spigot bend with 6" long riser. Then I install a slip on flange that slides over the pipe and down onto the floor, and if necessary cut the riser off to fit AFTERWARDS
  9. Redwood

    Redwood Master Plumber

    Messages:
    7,450
    Location:
    Connecticut
    Oh your only talking about 4" right at the toilet and then 3" at the end of the bend...
    Thats okay.
  10. zxed

    zxed New Member

    Messages:
    61
    Location:
    California
    Thankyou all.

    Is a hub x spigot also known as a hub x spg or 4x3 street 1/4
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