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Got a waste line leaking. Help!
18 August 2007


Q. I just discovered a small amount of water dripping from the black-- approximately 6 inches wide-- PVC drain pipe where it exits the ceiling in the basement. I checked the elbow and the water is coming from above that joint.

This is the toilet waste pipe that has the leak. I have this sinking feeling that the drywall from the first floor to the second will have to be torn out to locate the leak.

Is there another way of locating the leak without destroying the wall? If a plumber has to be called is there anything we need to be aware of? When he finds the leak is it a wise idea to replace the entire piping from the toilets to the basement? Where does he start to look for it? Is it possible that a copper pipe is leaking somewhere near the black PVC pipe? However when the toilet is flushed the small amount of water does increase ever so slightly.

We just had a major flood in the basement due to a $1.00 gasket going bad in the water treatment tank and now we are facing this. Our home was built in early 1970. Help!

A. You are probably seeing water dripping from the waste line at the point where the line turns from vertical as it comes down through the wall to the near horizontal as the pipe then leaves the house to the sewer. It’s only slightly possible that there is a nearby copper line leaking near that pipe allowing water to follow the larger pipe down on the outside of the pipe. But let’s rule that out on the basis that a copper pipe is a supply pipe that is under pressure and when they leak they leak all the time and what you are reporting is an intermittent leak. Leaking waste lines only leak when something-- such as a toilet, shower or sink-- is used and sends water through the pipe.

The good news for you is that I don’t think you’re going to have to start ripping wallboard off looking for this leak. PVC pipe is a great material that lasts and last and the joints are glued-- actually a chemical weld-- during installation. If they ha ven’t leaked in 37 years then the leak is unlikely the pipe or any of its joints. The leak is probably at the point of connection of something to that pipe and since you report that the leak increases in response to a toilet flush then I’m going to susp ect the toilet itself.

The part that goes bad over time and use with respect to the connection of the toilet to the waste line is the wax ring. When I inspect a toilet the first thing I do is stand over it with my legs astraddle the bowl. I grip the bowl with my calves and roc k back and forth to see if the toilet is loose at the base. Even a little movement over time will damage the seal and you can get leakage.

Replacing the wax ring requires lifting the bowl. For that you have to shut off the water to the toilet, disconnect the supply pipe, empty the bowl and reservoir tank of all water then unbolt the base from the flange and lift it up. Replace the wax ring and re-install the toilet carefully tightening the flange bolts not too tightly or you’ll crack the porcelain base.

While you’re at it, now would be a good time to replace that old 1970 three and half gallon or more flusher with a new 1.6 gallon per flush low flow toilet. The early models weren’t very good and I wouldn’t have recommended them but the newer ones are qu ite good. If you are not comfortable doing that yourself then that’s what you’ll pay a plumber to do. I’ll bet that will stop your water dripping from that pipe.

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