I just moved into a new home and one of the bathrooms has a pedestal sink. I can run the hot water, cold water, or both for extended periods and nothing leaks. But, if I put soap on my hands and then stick them under the faucet, I can immediately see bubbles hitting the ground under the rear of the sink. Hardly any water leaks at all, just soap! I've tried sticking my head back there to see where it is coming from but I can't tell!

Hey HO:

That is cause soap lags behind the waste a bit... fact is that you have a leak. Get a flashlight.. fill sink to rim and then drain. Get in there and see where that leak shows up... get back to us when have answer. Thanks... Mark.

Sounds like you have a very small leak in your drain line. It is probably occurring all the time but using soap changes the way it runs down a pipe and causes it to drip in a different location where you can see it. The leak will probably at the inlet or outlet of the trap. Unfortunately you will have to remove the pedestal of the sink to both locate the leak and to repair it. Repair will probably be just tightening the nut slightly. Try lifting the front rim of the sink and see it the pedestal can be slide out from underneath the sink. While one person supports the sink have another tighten the nuts on the trap.

I tried what you said but no leak showed up. I unscrewed the wall attachment and pulled the sink out; the leak came from where the porcelain meets a gray plastic tube.

Ok, you have a leaking drain assembly. If tightening the nut won't stop the leak, remove the drain assembly, clean around the drain hole and underneath the lip of the drain flange. Apply a bead of plumber's putty and reinstall. Look for crack in the sink it self around the drain hole.

Harold gets a gold star for this one. I read the problem and thought no body will get this but I knew what it was. Then I read harold who is dead on. The soap bubbles foam up in the verticle pipe above the trap causing the water level to be higher than if it were just water. The leak is in the first slip joint connection above the trap. Good one Harold! By the way, did you remember to use plumbers putty under the lip on the inside of the sink and the gasket on the underside of the sink? They are both fairly important.

Thanks Bob. Saw your brother the other day, wants that $10 you owe him.