Leaky sink trap

I've just installed a sink and am troubleshooting a slow drip. The drip comes off of the bottom of the trap. I had thought that the leak was coming from one of the slip nuts, but I held a dry paper towel around each one while water was running and while the drip was happening and it stayed dry in each case. I also held my hand over the trap while water was running and didn't feel anything dripping onto the trap from above.
My conclusion is that the trap itself is leaking, although I can't actually see or feel any cracks in it. I know that I often overlook other explanations in situations like this. Am I missing anything?
Thanks for your help, -Ben
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On Wed, 19 Sep 2007 04:53:56 -0700, Ben wrote:

Check alignment of pipes. Sometimes if the drain pipes aren't aligned, the connection isn't tight. You might also try wiping connecting surfaces to see if there are any burrs or crud to be removed. Any surface imperfection can also make things leak.
Finally, snug up the nuts but don't over tighten. Over tightening can strip threads on plastic and break nuts on metal.
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on 9/19/2007 7:53 AM Ben said the following:

Does this drip start after water has been sitting in the trap? Could it just be condensation from the cold water?
--

Bill
In Hamptonburgh, NY
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Is this a kitchen sink? If so, did you mistakenly install a drain basket for a cast iron sink onto a stainless steel sink? With the latter the threads on the basket do not go all the way up, so a thinner stainless sink will never get the basket tight enough, and the putty will be all that stops the water. The drip will always look like its coming from the P trap.
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Ben wrote:

With hope that you don't regard this question as an insult, is there a clean out plug at the bottom of the trap which might be the source of the leak?
Jeff
--
Jeffry Wisnia
(W1BSV + Brass Rat \'57 EE)
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If this is a bathroom sink, the pipe that forms the "basket" for the popup may be leaking. In other words the pipe that enters the bottom of the sink. Those can be a pain to seal. Plumbers putty dont always do the trick. After dealing with this problem several times, I put silicone around the pipe before tightening the nut against the sink bottom. The popup (plunger) nut could be leaking too.
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Ben wrote:

If it's a brass/chrome trap, you just may be right. Often, the brass will dissolve away from the inside, leaving a very thin shell. Forces exerted on the trap while re-installing then crack the brass in a hairline which may be very difficult to spot, glasses or not.
Take the trap off again and twist it with both hands. If it's corroded it will collapse.
Jim
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On Wed, 19 Sep 2007 04:53:56 -0700, Ben wrote:

If it's new, take it back and have it replaced. Make sure first that everything is assembled right and not misaligned and bound up when it was tightened.
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ahh they always leaked for me, cheap chincey junk quality.
havent had a leak in over 10 years after paying plumber to fix one. I do what he did.
Dry fit everything so it goes together OK
Mark so its easy to disassemble
Take apart and silicone bathtub caulk all fittings.
no more leaks ever, easy and stuff peels off if necessary
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