Drippy drain on new sink

Hi all,
I just installed a new counter with builtin sink made of mezanite and after I installed the faucett and sink drain, there is a slow drip when using the sink.
The sink is odd in that it has no vent for the drain, it is a simple bowl with a hole in it. The drain pipe is made of some plastic material with a rubber gasket that goes under the sink and tightened by a large nut on the pipe. The pipe does have holes near the top which I assume are there to accomodate a vent/overflow, which my sink does not have.
Instructions that came with the pipe said to use teflon tape on the top of the pipe which threads onto the shiny flange peice on the inside of the bowl. I have done this twice. Second time, I used the thicker teflon tape and it still drips. I am afraid of overtightening the nut to stop the drip. Is it possible that the drip is coming from the lower part of the pipe, where the big rubber gasket is? Should I teflon tape there too?
I was also thinking of doubling up with pipe dope and tape.
Any suggestions, other than 'call a plumber', will be appreciated. This is not rocket science, I just need a pointer or two.
Thanks,
Larry
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-- This is not rocket science, I just need a pointer or two.
If this *were* rocket science, you would use duct tape, not teflon tape.
That said, it would help if you knew exactly where the leak was. Is it possible to wrap rags or paper towels around the various junctions of the drain to determine where the leak is? If the upper most rag gets wet first, then you've isolated the problem area, and so on. Let us know.
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Thanks for the reply DD.
It's definately coming from the part closest to the bottom of the sink, ie the junction where the rubber gasket is supposed to seal it, or possibly leaking down the threads through the gasket and nut which holds the gasket.
Part of the problem is, even though there is likely a good seal inside the bowl, the vent holes in the pipe are there which will overflow water to the outside of the pipe and is likely dribbling through along the threads and past the gasket. I think if I put some dope and tape where the pipe threads through the gasket and nut, that would stop it?
Thanks,
Larry
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GoHabsGo wrote:

The rubber gasket will rarely provide an adequate seal. Use a smear of silicone sealant on both sides of the gasket (dry surfaces first). Use the same sealant on the fine threads of the tailpiece.
Don't worry about the lack of an overflow; that alone won't create any leakage.
Jim
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Yup, I've seen numerous drain installation instructions give bad info, as if they copied it from other bad sources. Often sinks have a rubber seal that can't quite squish into the roots of the threads. So the water follows a helical path down the threads and leaks out. It's a dumb design. Silicone it.
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Jim did a good job, follow his advice and that should handle it.
--
Joseph Meehan

Dia \'s Muire duit
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A real plumber would just take an exceedingly large wrench and tighten until the leak stopped or something snapped ;-)
Seriously, you're probably undertightening the thing, but only you can know/feel how far you're pushing it. I certainly don't want to goad you into breaking anything. Just get everything seated as well as you can with liberal amounts of teflon tape and then tighten as far as you feel comfortable.
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