leaking p-trap joint

The P-trap under my kitchen sink disintegrated the day after Christmas. Simple DIY repair. No big deal.
I replaced the metal trap with a PVC trap, figuring it wouldn't rust out or leak ever again...
I can't get the joint where the P-trap enters the copper drain stack to stop leaking. It's leaking out around the sealing washer, NOT the threads.
Tightened the nut. Still drips.
Replaced the PVC nut with a metal nut and rubber washer. Still drips.
Do I need to go back to a metal trap?
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On Jan 24, 11:44am, snipped-for-privacy@rochester.rr.com wrote:

The washer is the seal not the threads so that is suppose dotbe where it leaks. You really have a copper drain? That's pretty unusual.
I'd check the condition of the surfaces where the gasket goes. I'm guessing that one of the surfaces is patr of the original plumbing. You may need to clean it up a bit with some sand paper.
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Yes, the washer is definitely not sealing. Water's coming out from between the washer and PVC pipe, no matter how much I tighten it.
It's definitely a soldered COPPER drain stack. The guy that built this house certainly had some odd preferences.
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On Jan 24, 11:44am, snipped-for-privacy@rochester.rr.com wrote:

Not odd at all. That was code back in the 1950's and earlier.
Consider making the copper pipe round again by using a common tailpipe expander such as auto shops use. Odds are it is oval right now and further tightening just isn't going to work. You may have to cut off the oval section and solder in a coupling and new round section. If you do, try to find some Type K heavy wall for replacement. Good luck.
Joe
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On Jan 24, 11:44am, snipped-for-privacy@rochester.rr.com wrote:

Probably the old nut you took off had a built-in washer. I too have copper drains and the nut that goes on the end has a thin piece built- in that hits the tapered portion inside the drain pipe and gets forced against the inserted pipe. If the fitting on the inside end of your copper drain is cone shaped (gets smaller as goes in) the plastic tapered washers and the flat rubber washers are going to be tough to get a seal. You may need to dig through the trash and find the old nut. They still sell those fittings at the Borg and any plumbing supply house.
I've on occasion had to trim the 'seam' on the PVC pipes with a utilitly knife. Sometimes they stick out just enought to prevent the washer from sealing against the side of the pipe.
There is also a pipe dope specifically made for PVC pipes that helps them slide easier and seal better. If you go this route make sure the stuff you get is OK for use with PVC.
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Ah, that may be the problem...
Unfortunately, the nut was seized on to the copper fitting, I couldn't move it with an 18" pipe wrench, so I had to split it off. The nut is no more.
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snipped-for-privacy@rochester.rr.com writes:
| > Probably the old nut you took off had a built-in washer. I too have | > copper drains and the nut that goes on the end has a thin piece built- | > in that hits the tapered portion inside the drain pipe and gets forced | > against the inserted pipe. If the fitting on the inside end of your | > copper drain is cone shaped (gets smaller as goes in) the plastic | > tapered washers and the flat rubber washers are going to be tough to | > get a seal. You may need to dig through the trash and find the old | > nut. | | Ah, that may be the problem... | | Unfortunately, the nut was seized on to the copper fitting, I couldn't | move it with an 18" pipe wrench, so I had to split it off. The nut is | no more.
You could cut off the fitting and use a Fernco coupler. They make a special one just for copper to tubular: the 3010-150. Or you could solder on a new Marvel adapter. I was surprised to see that Home Depot actually carries these in bronze. You might even be able to use the nut from one.
                Dan Lanciani                 ddl@danlan.*com
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On 24 Jan 2011 21:43:07 GMT, ddl@danlan.*com (Dan Lanciani) wrote:

fittings. If the copper pipe is nor perfectly round and smooth, and if it is not VERY close to the same diameter as the plastic pipe the coupling is made for, it WILL leak. I believe there is a special coupling made to connect to copper - and there is definitely a copper/brass fitting made to transition to ABS - which needs to be soldered on. The "fernco" is also an option, of course, but it will alwoys look like a "band-aid" solution.
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you bump them, and they scream "ugh!!", to me. They DO need to be the right size, and it is still a good idea to have a good clean sealing surface. One of the rubber traps I installed always had a minor leak - untill I got around to replacing it with a proper ABS trap, properly glued together with the correct adapter fittings.
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Thanks guys, but my problem isn't with the trap itself.
It's where the trap enters the drain stack in the wall.
The leg of the P-trap enters the copper drain stack through a tee fitting. A compression nut threads on the copper tee fitting to seal the two together.
Originally, I had this sealed with the vinyl washer and plastic nut threaded on to the copper tee. Leaked a steady stream, no matter how tight I made it.
The metal nut with soft rubber washer is better, but it still drips.
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On Jan 25, 11:41am, snipped-for-privacy@rochester.rr.com wrote:

If I understand you the plastic pipe goes inside the copper and the rubber is being compressed into the copper and against the plastic pipe? I would install just that joint and test how firm that rubber washer is being compressed by trying to pull on the plastic piece.
If it pulls out easily then the rubber is not beeing compressed enough and you could try to find something to put behind the rubber so that it gets compressed further.
If it is hard to pull out then surface irregularities may be your problem. Make sure the copper is smooth and clean where the rubber goes up against it. Same for the plastic.
As a last resort you could coat the rubber washer with some pipe dope before installing. Let it sit a day before trying.
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On Mon, 24 Jan 2011 08:44:17 -0800 (PST), snipped-for-privacy@rochester.rr.com wrote:

If you get a good firm fit with the nut, I'd just dope it up where it's leaking. There's no pressure, and any waterproof dope that dries flexible will work. I used to use something called Liquid Rubber for troublesome drains, and it always worked easily. Came in a small tube that lasted forever. Don't see it around now. Probably butyl rubber. White silicone bathtub caulk works too but it isn't as sticky as the Liquid Rubber so you need a wider bead, and you should let it cure before using the drain.
Some of these PVC fittings aren't formed to fit older metal fittings well, or even other non-matched PVC fittings. The washers are different thickness and shape depending on what pack you grab, etc. Flanges are different thicknesses too. Just did my concrete basement tub and the PVC tailpiece flange and the washer combined were way too thick for the nut to grab enough threads, so I had to go pick up a metal tailpiece. Didn't have to use dope, but I wouldn't have hesitated.
--Vic
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