Toilet (Closet) flange and drain pipe sizing and type.

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Leif, Oct 4, 2020.

  1. Leif

    Leif New Member

    Joined:
    Sep 16, 2018
    Location:
    Florida
    I am building a house where the living area is on a second story level over a garage. There are two bathrooms and they are both upstairs. The living area floor is precast concrete and I am getting ready to do my plumbing rough in. The underground plumbing is a 4" PVC pipe that presently comes out of the garage slab and sticks up a few feet. I am wondering what size toilet drain pipe and size of the other drains for showers and sinks. I need to rent a core drill and bits. I don't know if you drill an exact size opening in the concrete or if you oversize it a bit. Any advice is greatly appreciated.
     
  2. Sylvan

    Sylvan Still learning

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    Sep 23, 2004
    Occupation:
    plumbing - fire suppression - boiler inspector
    Location:
    New York
    I always use 4" but your local code may allow 3" for the toilet and other fixtures
     
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  4. Terry

    Terry Administrator Staff Member

    Joined:
    Aug 17, 2004
    Occupation:
    Plumber
    Location:
    Bothell, Washington
    You will want to oversize the holes some. Have some pipe on hand so that you will know the sizing you will need.
    Where I'm at we run up to three toilets on 3" and on the 4th bump up to 4". Sewer lines outside the home have been 4" here.
     
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  5. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    Same here I have heard of inspectors allowing a 4th w/c addition without requiring increasing pipe size. a well installed system with proper grade etc aint going to notice a toilet added
     
  6. Leif

    Leif New Member

    Joined:
    Sep 16, 2018
    Location:
    Florida
    Do I gain anything by stepping down to 3". It appears the Oatey flange is for 3 or 4 inch and goes inside or outside the drain pipe depending on the pipe size. I think that would mean I still need a core drill big enough for the toilet flange as the determining factor. Do any of you have advice on what toilet flange part number to use?
     
  7. Master Plumber Mark

    Master Plumber Mark Sensitivity trainer and plumber of mens souls

    Joined:
    Feb 6, 2005
    Occupation:
    Sensitivity trainer.. and plumber of mens souls
    Location:
    indianapolis indiana - land of the free, home of

    Yes, you will gain a whole lot of elbow room to work with if you step it down to three because working with 4 inch pvc in -between rafters can be very challenging , tight and really not worth it if you are only installing 2 toilets anyway..... reduce it down to 3 inch and it can do everything just fine for even up to a 3 bathroom situation.... In our state you can do up to 4 toilets on a vertical 3 inch pipe.... .it will work fine as long as you have good enough fall.....
     
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  8. Jeff H Young

    Jeff H Young In the Trades

    Joined:
    Feb 27, 2020
    Location:
    92346
    Im with Master Mark on this easier to work wit 3 inch and it performs fine . Is bigger better probebly but in 99 percent of cases youll never know . So if its easy enough go ahead and run 4 . I wouldnt but your the boss !
     
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