Bathroom sink leak -- but an unusual case!

I recently installed a bathroom sink/vanity. The problem is with the drain. There was a small defect in the porcelain -- the hole on the underside/bottom of the sink wasn't perfectly circular, but had a small chip in it. So when I put the gasket+washer+nut on from the bottom, the gasket wasn't big enough to cover the hole (because of the chip). Silicone caulk around the perimeter worked for a few days, but then lots of water on the floor. What to do? I'm not removing/returning the sink! Do I remove the tailpiece, etc. and try to repair the porcelain? If so, with what? Do I try to find a bigger gasket? Do I use some kind of sealant/epoxy/spray foam on the already assembled joint? We are talking a fairly small gap... Help!
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I'd try plumbers putty If put on thick it should fill any voids like this and cheap Bob

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I don't like the putty solution -- what would prevent it from eventually falling off?
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its made specifically for sealing drain pipes to basins so I would assume it wouldn't fall off I've used it without problems before Bob

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"Silicone caulk around the perimeter worked for a few days, but then lots of water on the floor. What to do? "
Where did you put the silicone? On the gaskets and the small void before assembly? Or around the perimeter after assembly? It should be the former, which I would think would be the best alternative.
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I've used plumbers putty on a few installs (old habits die hard). However on one commercial install, I used a dap of expanding insulating foam. Spray a small amount on from the bottom. Stuff sticks like hell. If any comes out on top, let it cure, and then cut with a small razor, and you can maybe even touch it up with some glossy paint to match color. You can also use the epoxy based putty, shich is similar to the stuff used to patch leaking Gas tanks... Stuff hardens like a rock, and sticks pretty nicely on various surfaces.
-Tony

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snipped-for-privacy@rcn.com wrote:

More silicone!
Make sure the surfaces are dry. Use a hair dryer on the porcelain.
Apply caulk to both sides of the Mack washer. Apply caulk generously to the *threaded* part of the tailpiece. Yes! If you don't, water will spiral right down the threads.
If you use a big enough glob of caulk to fill the void in the porcelain, and let it harden, this repair should last forever.
Jim
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I'm not sure its so unusual. Plumbers Putty is made for this exact thing. Remove the tailpipe, spread some around the china, re-insert the tailpiece and let the putty squish out as you crank down the nut on the bottom. The bottom gasket is just to keep metal from touching the china, not for leaks. No caulk needed on nut either, There should never be water at the nut itself if installed properly. Should also never be need for caulk in such an install.

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