Tailpiece extension downstream of wall tube?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by DavidTu, Jun 11, 2012.

  1. DavidTu

    DavidTu Member

    Messages:
    239
    Location:
    Seattle, WA
    I have an old-old cast iron double-bowl laundry sink in the basement against an exterior wall. The bowls are about 25" apart. I am thinking I can get a Continuous Waste Kit (or make one) to connect the bowls and go into a P-trap. The sink will sit in a shallow alcove and so at this point the drain (wall tube) will pass through the alcove side wall (drain still running parallel to the exterior wall). The tricky part is that the old cast iron drain has a threaded sani-T with a 1-1/2" nipple threaded into it. Can I simply connect the wall tube into a slip-joint coupling and then go to a direct connect tube to the nipple? The direct connect is what the original implementation was. However, I have read that it is "not OK" to have any tailpiece extension after the wall tube? Is that true? What is the purpose/meaning of this?

    In any case, please see the attached diagram and see if what I have flies... if not please advise.

    Diagram notes:
    For reference, I have included letter labels for various parts on the diagram (A-K) please refer as needed. There are two alternatives based whether I can find a Continuous Waste kit (CW-kit): B-2 uses a 90-deg coupling instead of a CW-kit and D-2 uses a Tee Coupling instead of the CW-kit.

    Thanks!

    Attached Files:

  2. Terry

    Terry Administrator Staff Member

    Messages:
    15,110
    Location:
    Bothell, Washington
    The correct procedure would be to to replace with a longer nipple, or extend the nipple with a second nipple and coupling. .
    The slip joints are allowed only where they are accessible. Why hide something that can fail?
  3. hj

    hj Moderator & Master Plumber Staff Member

    Messages:
    26,797
    Location:
    Cave Creek, Arizona
    Slip joints can leak and come apart. In addition, that "double slip nut coupling" you start with is not permitted because it has a "backward" joint which will catch debris. A good plumber would use rigid piping from the galvanized to the trap.
  4. DavidTu

    DavidTu Member

    Messages:
    239
    Location:
    Seattle, WA
    OK. I don't have a die to cut threads into rigid steel pipe so I will have to transition from the nipple to plastic somehow... what is the connection for doing that? Can I just get a female ABS adapter? Does that take pipe dope?
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