Locating the source of a leak and fixing the problem is best accomplished through a process of elimination. In most cases, the cause of the leak will be in the area where there is a sink or toilet nearby, and water may be escaping through a faulty seal or a bad connection. In this event, a simple visual inspection while running water in the sink or flushing the toilet will likely expose the problem.

Things You Will Need

Patience and Persistence.

Step 1

Typically, there are a hot and cold supply line under a sink and a single supply line that connects to underside of a toilet tank. These lines have small gaskets inside the fitting that will harden over time. When this happens, water will drip or spray continuously, and the leak will become worse if the lines are not replaced. Since these supply lines are fed through an angle stop valve, closing the valve will likely be all that's necessary in order to replace the line.

However, if the valve is not seating fully, it will be necessary to close the main shut-off valve that services the house or the individual unit, as may be the case with an apartment or an office space. To check the angle stop valve, close it completely and run the water at the faucet, or by flushing the toilet. If water is getting through, it will be necessary to change the angle stop valve in order to replace the supply line.

If the supply lines or angle stop valves are not the problem, the water may be escaping through a faulty seal at the base of the toilet, or ring gasket at one of the P-trap connections under the sink. Running the water or flushing the toilet several times will most often disclose this problem.

If water is escaping from the underside of the toilet, the wax ring that seals the connection between the toilet and the waste hub will need to be replaced. If water is escaping between the toilet bowl and the tank, the tank gasket has probably become brittle or deteriorated. In either case, it will be necessary to shut off the water in order to replace these gaskets. Flush the toilet several times and sponge any remaining water from the tank and bowl before removing the toilet.

If water is seen dripping from the P-trap or the underside of the sink, this assembly will need to be removed and inspected. In many instances replacing the ring gaskets and nuts will solve problem with a P-trap. Be sure to replace these at all connections, including the stub-out connection to the drain line. Following these basic steps, you should be able to isolate and repair any basic plumbing leak.

Tips & Warnings