[LazyPup]

I was fortunate enough to have taken my apprenticeship under the Master Plumber who pioneered the idea of video inspection. While I do not currently have the equipment I do have a very close friend who does and i have rented his equipment on a couple occassions.

If you happen to have cast iron soil pipes, i can offer some informaton that may help you locate the problem.

A bathroom vanity bowl (bathroom sink) requires a 1 1/4" drain line. Although there is 1 1/4" cast iron pipe, it was not commonly used. Instead the put a reducing Wye on the branch line that has an 1 1/4 threaded side opening. The line was then run with 1 1/4" galvanized iron pipe.

While there are instances of the pipe wall corroding through, the most common point of corrosion occurs at the threaded joints where the zinc coating was cut away from the pipe during the threading process.

If you know where the drain, waste & vent stack rises up through the wall you can pretty much guess the layout. first imagine a line from the toilet to the stack, that should be the main horizontal branch for the bathroom. Next imagine a line straight down from where the sink drain connects to the wall. Depending upon the clearances, the line from the base of the sink riser to the horizontal branch will either run at right angles to the branch or at a 45deg angle from the base of the sink riser to the point where it joins the horizontal branch line. The 45deg angle will be in the direction of the downstream flow from the toilet.

i would begin by pulling the lavatory bowl cabinet away from the wall and opening the wall behind the cabinet. It would be easy to patch that hole and it wont require a finish as it is concealed behind the cabinet. If necessary, you could make another access hole in the floof under that cabinet, which again would be concealed by the cabinet.

Once you have a hole, get a small mirror ( i carry a ladies makeup mirror with a plastic frame about 2 x 5 inches). Hold the mirror inside the wall or floor cavity and shine a flashligth directly onto the mirror, it will reflect the light into the hole on your line of sight and you can see the results in the mirror.

Once you have located the leak in that manner, you will know exactly where you have to make an access hole to solve the problem.

If the problem is a corroded galvanized iron pipe, the best solution is to replace it with PVC.

If the galvanized pipe is leaking where it threads into a section of cast iron pipe, you can cut the galvanized off about 1/4" to 1/2" inch from the cast iron. You can then use a hammer and a punch to fold one wall of the remaining galvanized in toward the center of the pipe to loosen it. Once it is loosened enough to remove the stub of pipe, clean the threads of the cast iron with a wire bruch, apply pipe dope to the threads of a Male PVC thread adapter and screw the adapter into the cast iron, then you can run new PVC from that point back to the sink.