Replacing cast iron with ABS for drains?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by Ken souza, Feb 15, 2020.

  1. Ken souza

    Ken souza New Member

    Apr 12, 2018
    Northern California
    So I am replacing old cast iron drain pipes with ABS, I have a few questions one regarding the toilet drain pipe, when I install all the new ABS with the fittings everything is perpendicular or square so how do you create a slope without that affecting everything else? I have a picture of what I am doing hopefully someone can chime in, also is the toilet flange pipe “horizontal” OK to be level, I figure with the force of water flushing from the toilet it would not need a slope to drain.

    Attached Files:

    Last edited by a moderator: Feb 16, 2020
  2. Terry

    Terry Administrator Staff Member

    Aug 17, 2004
    Bothell, Washington
    The fittings have the slope built in. You can take your level and put everything to a 1/4" per foot grade. There is also a bit of slop in the joint when they are glued. It's a solvent that make the fitting looser.
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  4. Reach4

    Reach4 Well-Known Member

    Sep 25, 2013
    I think you plan to put a closet flange under the plumb bob.
    I think all of the ABS in the picture is there for mockup purposes.

    You could use a 4x3 closet elbow to mount the closet flange. [​IMG] It could accept a 4 inch outside or inside flange.

    Ideally your 3 inch pipe would cut the corner, and connect to a wye in the main drain line. Alternatively, you would use a 45 to a wye, or use a combo which combines a 45 and a wye. That may be a combo you have pointing up at the moment. The tilt of the wye establishes the slope to give you your 1/4 inch per foot.

    You may or may not have to add more venting, depending on what is upstream. If upstream is all bathroom stuff, you will probably not need to add toilet venting. I am not a plumber.
    Last edited: Feb 16, 2020
  5. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

    Sep 2, 2004
    Retired Systems engineer for defense industry.
    New England
    FWIW, cast iron is still a premium product. Be prepared for your drains to be louder.
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