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Leaky waste pipe

I have a leak in a waste water pipe which manifests itself by dripping water onto my concrete basement floor. The water appears to be running down the outside of the vertical pipe that comes through the subfloor (ceiling of my basement)and makes a 90 degree turn to the horizontal pipe running out of the house. This vertical pipe takes the waste from the second floor of my two story house. Since this pipe is behind a wall on the first floor and runs above the ceiling in my first floor I can't see where the leak originates. Any suggestions on how to decide where to start cutting holes in the sheetrock. Do I start in the wall or in the ceiling.
Thanks in advance for any suggestions.

Re: Leaky waste pipe

I would start with the first floor wall if I had to. A couple questions to check out before cutting into the drywall since it may help narrow down where to cut. What kind of drain pipe is it, PVC, copper, cast iron? How old is the drain pipe? Are there any supply pipes in the same area as the drain pipe? Does it only drip when tub is emptied or toilet flushed or does it always drip?

If the leak was above the ceiling, I would think you would see a wet spot or have a drywall seam start to bubble on the ceiling if the leak was there. Some of the leaky water would drip off the pipe in the ceiling cavity before running down the vertical.

It could be that a drywall screw or a screw used for a wall hanging has punctured the drain pipe and after a while it has rusted away enough to allow the leak. Is there anything hanging on the wall in the vicinity of the drain pipe?

It could also be where a 90* fitting is connected to the vertical section of pipe at the wall / ceiling 90*. If the vertical pipe isn't supported well enough gravity could have pulled it away from the 90* fitting. Is there any play in the drain pipe in the basement where the vertical pipe goes into the 90* that allows you to raise it an inch or two? (maybe resetting the vertical back into the flange of a 90* up above)

Just some ideas to think about before cutting into the wall. Hope this helps.

Re: Leaky waste pipe

bp21901 thanks for you input.
Your comments about starting in a wall makes sense since I don't see any evidence of dripping water on my ceiling. The pipe is PVC. The comment you made about the pipe possibly being punctered by a nail or screw really caught my attention. The wall containg the vertical pipe is in an alcove that contains our washer/dryer. These appliances are behind folding doors and my wife has used this wall to hang all kinds of hooks for dust pans, flash lights, etc. It is very possible she hit something at some point in time.
In any event this wall is where we will start.
Thanks again.

Re: Leaky waste pipe

Good luck, I hope you find it quickly. Looking for a leak behind drywall is no fun. At least you can open it up in the W/D alcove rather than a highly visible wall in the LR or Kitchen. My standards for my personal drywall taping and mudding are a little lower in a laundry room than in a living room so the repair would go a little quicker for me! :)

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