I found a water drip leak on both edges of a 3” PVC pipe-coupling located over my basement ceiling. The pipe runs horizontally above a bathroom closet with another PVC pipe running just adjacent and a couple of copper pipes under it. I can put my hand up through a hole in the drywall and access the coupling but don’t think it will be straightforward to cut and replace.

Not sure what the pipe is carrying but it appears that it is venting my furnace exhaust to the outside. In the winter I turn on the whole-house humidifier and I am wondering if water is condensing in the pipe and dripping out (one drop about every 1-2 min).

First, does this sound reasonable? Any chance there is a safety risk? (I have a carbon monoxide monitor on every floor including the basement and it hasn’t gone off)

Second, any suggestions on how to fix the leak would be appreciated. Can I use putty over the coupling joint like the JB Weld water weld? Is there a better product that I should use?

Thanks! Leaking coupling

  • pvc solvent will melt the pipe together you should just be able to paint it around the joint and have it seal up. i've done this will abs for a slow leak. the biggest the gob the better the job. you could also use a hub saver to remove the stop in a 3" pvc coupling slide it on the pipe and glue it all up and slide it back on. i'd try just putting it around the joint again first. Commented Jan 29 at 1:07
  • Assuming this is the HVAC exhaust vent pipe, the water is not coming from your inside air, humidifier, etc. It is from water vapor in the exhaust condensing and dripping down and finding a convenient hole to drip out. This condensate is inevitable on modern furnaces because the exhaust is much lower temperature than it used to be. So the issue (as always with HVAC condensate) is making sure it goes where it should and doesn't go where it shouldn't. Commented Jan 29 at 4:29
  • It is dripping because it is full of water. I think your assumption about what it is , is incorrect Commented Jan 29 at 5:34
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    @FreshCodemonger to seal the joint the OP will need to ensure the joint is dry. Perhaps during spring when the HVAC isn't running, he can aim a space heater at it to make sure it's fully dry and then slather the solvent on. Hopefully he can access the entire circumference. Also, would be worth wrapping the pipe with toilet paper to confirm that the leak isn't happening elsewhere and traveling along the pipe to the lowest point—the coupler.
    – Huesmann
    Commented Jan 29 at 16:20
  • Please take the tour so you know how to respond to answers.
    – isherwood
    Commented Feb 12 at 14:20

1 Answer 1


Likely that coupling was never glued to the pipe. It happens. Assuming some non-pressure application, such as HVAC venting: Try to pull the joint apart, dry the pieces, and reassemble using PVC solvent cement. Otherwise turn furnace/whatever off, try to suck out any moisture with absorbant tissue, apply PVC solvent cement all around the edges of both joints. That failing, guess you'll have to cut out the bad joint and rebuild.

  • Thank you all for your comments. I put PVC cement around the joint (Oatey PVC Blue Lava hot cement) where I could feel the drip and the leak seems to have stopped. Didn’t have to cut the pipe or disassemble the joint. Will see if it holds. Very much appreciate your help - peace!
    – lemerita
    Commented Feb 13 at 0:45

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