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 waste pipe? However, when the toilet is flushed, the small amount of water does increase ever so slightly.

We've had a flood in the basement before due to a gasket going bad in the water conditioner and now we are facing this. Our home was built in early 1970s, so I'm not surprised things are wearing out.

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 near horizontal as the pipe then leaves the house to the sewer or septic system. 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 haven't leaked in 40 years, then the leak is unlikely to be 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 suspect the toilet itself. You could put a dye tablet in the toilet, but I don't think you need to.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 straddling the bowl. I grip the bowl with my calves and rock 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. The replacement rings I like have a plastic flange that fits down the waste pipe as an added bit of protection and they are cheap.

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. I even ended up on ABC's "20/20" news show talking about how bad the early ones were, and there was a congressman out in the Midwest who was trying to get the law changed to bring the old bigger toilets back. Canada still has them.

The newer ones are quite good. You may have seen the Kohler TV ad where a young man spots a very attractive lady plumber entering the next unit in his row of townhouses so he runs into his unit and throws everything from dog food to potting soil into his toilet to get it to clog so he can call the cute plumber lady, but nothing would stop it up. The point of the ad is if you put it in that toilet, it will flush.

If you are not comfortable replacing the wax ring or the toilet yourself, then that's what you'll pay a plumber to do. I'll bet that will stop water dripping from that waste pipe.

Keep the mail coming. If you've got a question, tip, or comment let me know. Write "On The Level," c/o The Capital, P.O. Box 3407, Annapolis, MD 21403 or email me at jimrooney@jimrooneyon