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  1. #1
    Join Date
    Jun 2007
    Posts
    86

    Default connecting plastic and metal plumbing

    Our house is 40 years old so all our plumbing is metal. We had to temporarily remove a bathroom cabinet that houses the sink, and I tried to reconnect everything tonight. The cabinet is definitely not 40 years old, and the drain plumbing is plastic down to, and including, the trap. The part of the drain that comes out of the wall is metal (chrome) with a captive nut that screws onto the threads on the trap.
    That connection between the metal and plastic insists on leaking. It did NOT leak before I took it apart. I tried connecting it without teflon tape, I tried a normal amount of tape, and I tried a LOT of teflon tape. (It had teflon on it when I took it apart.) I tried just making it finger tight, and I tried using a wrench (first a little, then a lot).
    What's the trick to getting the metal-to-plastic connection to not leak?
    Thanks a lot.

  2. #2
    Join Date
    Jul 2010
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    SoCal
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    7,760

    Default Re: connecting plastic and metal plumbing

    Check the thread on the trap. With a captive nut, or when you have a slip joint washer, teflon tape is not needed, and if there was teflon tape before, it's a sign that it leaked before.

    If the thread on the trap is damaged, replace the trap.

    If the thread on the trap is fine, replace the waste arm. I prefer ABS.

    With any sign of a leak, it's a good idea to replace most of these very inexpensive parts.

  3. #3
    Join Date
    Feb 2010
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    1,257

    Default Re: connecting plastic and metal plumbing

    As stated by di1 replace the trap, including the chrome section coming from the wall. Use a plastic slip joint trap not a glue trap.

    John

  4. #4
    Join Date
    Jun 2007
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    86

    Default Re: connecting plastic and metal plumbing

    How do you replace the chrome part? What's on the other end of it? How is it connected?

  5. #5
    Join Date
    Feb 2010
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    Default Re: connecting plastic and metal plumbing

    The way you describe it should be part of the old trap. If that is the case there should be a slip nut holding it in place. A picture would be a great help.

    John

  6. #6
    Join Date
    Jun 2007
    Posts
    86

    Default Re: connecting plastic and metal plumbing

    Boy, this forum isn't very picture friendly! It keeps telling me my perfectly fine jpg file isn't valid.
    Okay, Finally!
    This is what I've got. You can see why I asked what's on the other end of the chrome piece.
    Note that the wall is closed up nice and tight and freshly painted; that's why we had removed the cabinet, so we could re-do the walls. So I'm not really too eager to take the cabinet back out and re-open the wall.
    By the way, I bought a straight piece to replace that bellows adapter and then found out last night that my new pipe has a larger diameter than the bellows so I just re-used it, in the mistaken belief that I would have the whole thing all finished last night.

  7. #7
    Join Date
    Jul 2010
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    SoCal
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    Default Re: connecting plastic and metal plumbing

    Your photo is good, but not good enough.

    It would help us if we knew what's behind the escutheon. Try to remove it so we can see how the chrome waste arm is attached to the drain in the wall. There are various ways to connect it. Then we can help you find the best solution.

  8. #8
    Join Date
    Jun 2007
    Posts
    86

    Default Re: connecting plastic and metal plumbing

    Quote Originally Posted by dj1 View Post
    Your photo is good, but not good enough.

    It would help us if we knew what's behind the escutheon. Try to remove it so we can see how the chrome waste arm is attached to the drain in the wall. There are various ways to connect it. Then we can help you find the best solution.
    Behind the escutcheon is just a ragged hole in the sheetrock. Not a big one, just an ugly ragged one.

  9. #9
    Join Date
    Jul 2010
    Posts
    62

    Default Re: connecting plastic and metal plumbing

    Use good quality sealant. We also had a similar problem in our bathrooms, we used the sealant, that closed the gap and the pipe works perfectly, although it is a temporary work, but it does the job very well and it lasts for a long period of time.

  10. #10
    Join Date
    Sep 2011
    Location
    Michigan
    Posts
    7

    Default Re: connecting plastic and metal plumbing

    Just a note, avoid using teflon tape unless you are using it going metal to metal ( except for gas lines). Teflon tape is a thread lubricant and NOT meant for sealing. When going from metal to plastic, use a sealant such as pipe dope. Amateurs typically start tape right at the end of threads and then put multiple layers of teflon on threads. This is incorrect. Start the teflon tape a thread or two from the end, pull snuggly in the direction of "tightening" and separate by pulling tight until the tape breaks.

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