Is the U-shaped drain pipe beneath your sink corroded or leaking? If that pipe, called a “trap” or “P-trap,” is leaking, either fix it or replace it with an inexpensive new one before water damages the area under the sink.
Look for where the drip is originating. In many cases, it comes from loose fittings, especially the coupling nuts that connect the pipe sections together.
You can often stop a drip by simply tightening the coupling nuts (shown in the illustration below). The best tool for this is a large pair of slip-joint pliers (also referred to as “tongue-and-groove pliers” or by the trade name, Channellock pliers (see photo). Open the jaws of the pliers wide enough to grip the coupling nut. Tighten the nut by turning it clockwise. Apply strong pressure but don’t strip the threads by over-tightening.
To fix a leaky sink trap, start by placing a bucket beneath the trap. Using slip-joint pliers, disconnect the coupling nuts that hold the trap to the tailpiece and drainpipe.
Be ready for water to pour out of the disconnected pipe momentarily. Once you have taken the trap apart, clean it out with a straightened wire coat hanger and replace any faulty parts.
When reassembling it, first tighten the coupling nuts by hand and then tighten them with pliers, but don’t over-tighten. Run the water, and look for leaks. If you spot leaks, tighten the nuts a little more. If everything appears to be sound, place a newspaper under the sink and check the paper for signs of dripping the next day.
How to Repair a Leaking Sink Drain Trap
If the leak is occurring at one of the joints between pipes, try tightening the coupling nuts.
On a metal trap, tighten them hand tight plus about a half turn, using slip-joint pliers to grip the nut.
On a plastic trap, just hand tighten, and, if needed, give the nut about a quarter of a turn with slip-joint pliers.
If that doesn’t work, loosen and remove the entire trap.
First, check the large rubber slip washers or cone-shaped plastic washers that provide the watertight seal at each joint between the trap’s pipes. Rubber washers may leak as the rubber hardens over time. If they’re hard or deteriorated, replace them. Plastic-pipe traps are more likely to leak when the pipes or washers become misaligned, so check for alignment.
Check the pipes for rust or corrosion. If s pipe is corroded or cracked, take it with you to the hardware store to buy an appropriate replacement. Replace the entire trap (PVC traps are inexpensive, durable, easy to work with, and don’t corrode the way chromed brass drainpipes do).