invisible drip

March 8, 2024 10:46 AM

There's an intermittent dripping sound in the ceiling below our 3rd floor toilet. It happens when someone sits on the toilet, and then after they flush. There's no visible sign of water, and our plumber has said it's probably dripping inside a pipe, and that we only need to worry about it when we see or smell something. I find this compelling, yet also, the dripping sound remains viscerally concerning. I'm asking the hive mind for perspective and possible insight!
posted by spindrifter to Home & Garden (8 answers total)

Given this starts when someone sits on the toilet, my first guess is that water is dribbling over the S-bend in the toilet itself as the toilet is filled (by a person or by the cistern)?
posted by caek at 10:49 AM on March 8, 2024 [2 favorites]

Toilets should be pretty solid; my first guess is that there's a slight wobble in the toilet, and when someone sits down it causes the toilet to shift just enough that either the fill valve trips for a moment, or a little water sort of burps over the S-bend. If the toilet rocks or shifts, either when gently rocked by hand or from body weight, the bolts connecting the toilet to the flange in the floor may need to be tightened or replaced. Sometimes, the bolts get corroded from the damp environment (whether that's from condensation, regular cleanings, floor moppings, whatever).

Might also check the fill valve; take the lid off the tank and sit on the seat (lid closed is fine) facing the back of the toilet. Does the fill valve open for just a moment, from the water shifting in the tank? There's usually a flexible tube running from the fill valve to the overflow tube, where water goes to fill the bowl after the tank flapper has closed and the tank is refilling. Are there maybe a few drips of water falling from that tube?

If you (or your plumber) is going to go so far as removing the toilet, perhaps to check or replace the flange bolts, always always always replace the wax ring that seals the toilet to the flange. They're so inexpensive, and nobody wants to clean up the fallout from that kind of leak.
posted by xedrik at 11:24 AM on March 8, 2024 [2 favorites]

Response by poster: I should say, at the start of all this, the wax ring was replaced and the drip stopped for a time but then returned.

I'll try xedrik's explorations and report back. Thanks for comments so far!
posted by spindrifter at 12:00 PM on March 8, 2024

Turn off the fill valve for the tank and flush the toilet with a bucket of water, which should leave not very much in the bowl

Then with more water from the bucket add just enough water so that air from the sewer can’t escape into the bathroom.

Then have someone sit gently on the toilet (to avoid causing sloshing in the bowl) and pee while someone listens from below. Since the total amount of liquid in the bowl at the end of this procedure should be well below the usual water line in the bowl, no liquid should have gone over the S bend, and if no dripping is heard, then the drip sound is indeed coming from within the pipe and you're in good shape.

If you do hear dripping during this procedure, I’d say you could have a problem.
posted by jamjam at 2:55 PM on March 8, 2024

Replace the first paragraph of my answer with the following:

Turn off the fill valve for the tank and flush the toilet, then with a bucket of water, flush the toilet again by pouring water straight into the bowl, which should leave not very much in the bowl.
posted by jamjam at 3:03 PM on March 8, 2024

I had something that sounds like this when I was using cleaning tablets ("1000 flushes" etc) that had some bad chemical in them, like bleach. Normal toilet cleaning stuff, but bad for, as it turns out, rubber. My flapper had started a march toward plastic, warping and stiffening, letting small bits of water through, and replacing it fixed the sound that had been mysteriously emanating for months, maybe years? I blocked it out.
posted by rhizome at 4:11 PM on March 8, 2024

>at the start of all this, the wax ring was replaced and the drip stopped for a time but then returned

Definitely check for the toilet being securely mounted. If the toilet can rock, then it can compress the wax when rocked, and then when the toilet returns to rest, the wax won't restore itself to re-seal with the toilet. This can result in a place for water (or sewer gas) to escape.

If you do pull the toilet again, one option would be to replace with a waxless ring, which is made of rubber or plastic. They are reusable if you repeatedly pull the toilet, and a side benefit of this is that they will hold their shape and re-seal against a rocking toilet. You still should make every effort to properly secure the toilet, but the waxless ring can help.
posted by yuwtze at 5:04 PM on March 8, 2024 [1 favorite]

Response by poster: We tried all of these and none of them seemed to provide an explanation, so we gave in and cut into the wall, where we did, indeed, discover water dripping down the outside of a pipe and hitting the ceiling from the inside. Why hasn't it seeped through?? Who knows! But the plumbers will come to investigate this week.

Thanks so much everyone for your thoughts! They helped us move this forward.
posted by spindrifter at 5:03 AM on March 12, 2024 [1 favorite]