Diagnosing a possible drain leak

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If the 20 yr old plumbing was done in PVC, dripping noises are common and may not indicate a leak.

A stud finder can be useful in locating wet plaster since it appears denser than the surrounding dry plaster. Try it.

An Ohmmeter might be used with a pair of probes to detect areas of lower than normal resistance. Takes some experimenting.

Touching the suspect area with the back of the hand can sometimes show up moist spots from the feel of it.

Jim

The water stain indicates a leak.

Whether it's actually the drips hitting the ceiling or inside the drain is of little consequence; the leak needs fixing.

As another poster said, investigate for dampness in the plaster and the ceiling area. If it is drain rather than supply, not using the suspect sink for a while should allow it to dry completely whereas a supply line leak would continue.

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The thing is the dark area on the ceiling is so small and slow-growing that I'm not even sure it's a leak. It's maybe 6 inches long and a quarter inch wide, along the edge where the ceiling meets the molding.

How long should I avoid using the sink to wait for it to dry?

I think the drain pipes are PVC, but if they're copper, does that mean a dripping noise definitely indicates a leak?

Jimmy

What else do you think it might be? Even if it's mold/mildew that would be indicative it's damp.

Get up there and see if the spot is damp to touch, slightly softened if actually plaster, etc., ...

The drip may or may not be inside the pipe; there's no way to tell from here as I can neither see nor hear it to judge.

If it's actually the water dripping on the upper side of the ceiling it may be possible to tell that by being close and listening carefully--the old mechanic's trick of the screwdriver touching the wall and using it as a stethoscope might help locate it if so.

Drips inside drains can occur w/ either Cu or PVC. If it's been a long time in the house and never noticed it at all until recently, it's likely a new symptom.

How long before the area dries out if damp would depend on many factors but I'd think a week would make a difference that should be discernible at most if it's significant at all...

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