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Thread: Connecting plastic sink drain to metal p trap

  1. #1
    DIY Junior Member DIYhell's Avatar
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    Default Connecting plastic sink drain to metal p trap

    Hello. I am installing a new vanity, sink, and faucet. The existing p trap is metal and the center of trap opening is 8" off wall. The new sink drain center will be 9" off wall and the drain is plastic. How do I connect the sink drain to the trap despite the difference in materials and the offset? I have read that I should connect metal to metal but I am hoping there is some way. Otherwise, I could use the metal drain off the sink that is being replaced, but the 1" offset is still an issue. Looks to me like the straight end of the existing trap is sweated over a copper stub that is secured with compression washer and nut to Sched 40 pvc drain pipe so I suppose that one solution is to connect a 1" longer new pvc trap to the drain pipe. Any other way? I would like to avoid opening up the wall to get to the nut and vertical pipe. Any guidance is appreciated. Thanks.
    Last edited by DIYhell; 10-05-2010 at 03:56 PM. Reason: more info

  2. #2
    In the Trades Jerome2877's Avatar
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    If its copper, cut it about 4" from the wall and use an abs copper slip joint adapter then continue with the plastic from there. They also make them in pvc if thats whats used in your area.

  3. #3
    Forum Admin, Expert Plumber Terry's Avatar
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    Normally you have a slip joint connection near the wall. Almost always I install a "new" p-trap when replacing a faucet or sink. I prefer working with new stuff. I can't warranty the old stuff, and it takes too much time to inspect and clean up something that cost so little to replace.
    You don't offset the vertical, you cut the p-trap as it goes into the wall fitting. The adjustment is made on the horizontal.

  4. #4
    DIY Junior Member DIYhell's Avatar
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    Thanks for responding. Looks like I have to dump the metal and go pvc to the vertical pipe in the wall.

  5. #5
    Moderator & Master Plumber hj's Avatar
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    You use slip joint fittings and there is absolutely NOTHING wrong with mixing the materials, since they are both the same physical size. Your only problem could come in if the pipe into the wall is NOT connected with a slip joint, in which case you have to cut the pipe out of the fitting in the wall, or have a plumber, who knows how to do it without damaging the pipe in the wall, do it.

  6. #6
    Master Plumber Redwood's Avatar
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    Mass Code does not allow slip joints on the outlet side of the trap...

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