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Thread: toilet drain 3" or 4"?

  1. #1
    DIY Member zxed's Avatar
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    Default toilet drain 3" or 4"?

    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?
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  2. #2
    Master Plumber Redwood's Avatar
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    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. #3

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    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 by iminaquagmire; 02-01-2009 at 07:03 PM.

  4. #4
    DIY Member zxed's Avatar
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    Quote Originally Posted by iminaquagmire View Post
    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.
    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 by zxed; 02-01-2009 at 08:55 PM.

  5. #5
    DIY Member zxed's Avatar
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    Quote Originally Posted by Redwood View Post
    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?
    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. #6
    Master Plumber Redwood's Avatar
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    It should be 3" all the way!

  7. #7
    DIY Member zxed's Avatar
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    Quote Originally Posted by Redwood View Post
    It should be 3" all the way!
    any clue why they (original home construction back in 1979) would install it the other way? 4" turning into a 3"

  8. #8
    Moderator & Master Plumber hj's Avatar
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    Default 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. #9
    Master Plumber Redwood's Avatar
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    Oh your only talking about 4" right at the toilet and then 3" at the end of the bend...
    Thats okay.

  10. #10
    DIY Member zxed's Avatar
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    Talking

    Quote Originally Posted by hj View Post
    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
    Thankyou all.

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

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