sink drain: use 'pipe thread compound' on abs pipe?

Discussion in 'Plumbing Forum, Professional & DIY Advice' started by outofplumb, Dec 7, 2008.

  1. outofplumb

    outofplumb New Member

    Dec 7, 2008
    Hi all,

    I'm replacing a sink in my bathroom and will need to redo the drain plumbing.

    Now the 2 fittings I have at hand are:
    - an adapter/reducer to connect the sink's 1-1/4 chrome tailpiece (compression fitted) to the 1-1/2 drain pipe (solvent welded), and
    - a 1-1/2 P-trap (solvent weld at both ends, with a "swivel nut" joint on one side of the "U").

    Just to make sure we're talking the same language, here's pictures that are visually similar to what I am talking about:
    - the adapter:

    In theory I can see how everything will be put together. But the problem I have is this: I have worked in the past with slip-joint fittings where there is both a nut and a beveled washer (nylon, I guess?); you slip the nut, then and the washer onto the one pipe, and then fasten the nut to the threaded adapter on the fitting.

    However, in both the fittings I have above, there are no washers. I can see that the inside of the nut does not have a flat end; it has a "lip" on it. On the other (threaded) side of the fitting, the inside edge is beveled inward so it seems that the "lip" on the nut fits on the inside of the fitting body. I suppose this is what compresses against the inserted pipe?

    So here are my questions:
    1 - Is that "lip" supposed to take the place of a separate washer?
    2 - Is this type of joint as reliable as a "standard" nut and washer arrangement?
    3 - What happens if I unscrew the joint, either during assembly or some time down the road? Is this type of joint reusable?
    4 - Is it suggested to use teflon "pipe thread compound" on this type of ABS joint? The compound I just bought is this:
    Will this make a better joint? Is this safe on ABS?

    Hope this is clear. Please ask if you need more info.


    Attached Files:

    Last edited by a moderator: Dec 8, 2008
  2. hj

    hj Moderator & Master Plumber Staff Member

    Aug 31, 2004
    Cave Creek, Arizona

    You are trying to connect apples to oranges with the fittings you show. That trap is 1 1/2" ips. If you used it, which I NEVER would, you have to connect it to the pipe from the wall, and then use the adapter at the sink to connect to the tailpiece.
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  4. jimbo

    jimbo Plumber

    Aug 31, 2004
    San Diego
    The nut on those fittings has the slip joint seal integral with it.

    The trap uses a "ground union" type seal.

    No tape or joint compound should be used on either of these.
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