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

    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

    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.
  3. jimbo

    jimbo Plumber

    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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