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Thread: Toilet drain slope

  1. #1

    Default Toilet drain slope

    Hello all,

    New member, first post after reading this site for some time on and off.

    I'm re-plumbing the toilet drain into the stack after moving the toilet. I've got about 18-inches from flange to stack. Using 3" ABS.

    On the subject of ensuring adequate slope (min. 1/4" per foot, but I'd like to go 1/2"), I note that when I seat 3" pipe all the way into a 3" elbow or wye, they fit really really close tolerance, with no room for cheating on the angle of connection. So, if my stack is vertical, the wye inlet is going to be horizontal, not slightly angled up. And if my closet flange is flat on the floor, the outlet of the elbow below it is going to be exactly horizontal, not slightly sloped down.

    I can see maybe over an 8-foot run there's some play or flex in the pipe, but zero of that on 18-inches of 3" pipe.

    So how am I going to get any slope out of this when I install it?


  2. #2
    Moderator & Master Plumber hj's Avatar
    Join Date
    Aug 2004
    Cave Creek, Arizona

    Default slope

    The fitting has the slope built into it, but regardless of how tight the joint seems, once the glue is applied there is a great deal of flexibility in the joint. You do not need 1/2" slope in the first place, however.

  3. #3


    Ya, I wondered about dry fitting versus glued fitting. Thanks.

    Not to sound thick or anything, but which fitting has slope built into it? I'm using a standard 90-elbow and santee wye.

    Oh, and thanks for the heads up on the slope - been reading since my post and understand now that 1/4"min to 1/2" max is optimum for "floating" the stuff along, unless I can get over 45-degrees.
    Last edited by bob_555; 01-09-2009 at 06:22 AM.

  4. #4


    Holy crap, Batman! I just put my square on both the elbows and the wyes, and they both have an exactly 1/4" per foot (1 in 48) out-of-square between the ends. Very cool. So all drains and vents are going to automatically have this slope built into them if you let the piping take its natural course as you build it up.

    Thanks for the pointer in the right direction.


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