A p-trap is a pipe attached to a sink drain that is shaped like the letter P. It is composed of two pieces. The straight pipe, known as the wall bend, enters the wall, while the curved part of the trap is known as the J-bend. The latter connects the former with the drain extension.

Like other plumbing pipes, the p-trap can leak, and a faulty gasket is one of the reasons why it does. If you find that the p-trap under a sink in your home has become leaky for the reason given above, you need to install a new gasket to the p-trap. Here are the things you should do to properly install the new gasket:

1. Get a bucket and place it under the sink to catch any water that still in the P-trap.

2. Use water pump pliers to loosen the slip nut, which you can find on the wall bend. The slip nut can be loosened by turning it counter-clockwise.

3. Pull the J-bend loose and twist the wall bend counter-clockwise to take out the p-trap.

4. Get your dry cloth and use it to clean wall connection threads.

5. Have a gasket and slip nut placed on the drain extension. A bevelled cone gasket should be the type used for p-traps made of PVC while a square slip joint gasket should be used for traps made of metal.

6. A slip nut should then be placed on the wall bend on the seal which connects to the trap. Put another slip nut on the same wall bend before placing the right gasket on it.

7. Have the wall bend placed in the wall connection. Afterwards, put the slip nut on the threads and turn it clockwise without tightening it.

8. The J-bend should then be placed on the drain extension and properly aligned to the wall bend. Then use your hands to turn slip nuts clockwise. The slip nut that is on the wall bend should then be tightened, and all slip nuts turned a quarter turn using pump pliers.

9. Switch the water tap on and check the p-trap for any leaks. If it is leaky, then get the nuts loose and have the joints realigned. Tighten slip joints and check for leaks afterwards.

Like all plumbing-related tasks, there is no substitute to having the right tools and safety equipment, so if you don’t have any of the tools mentioned above and safety gear like face masks and safety goggles, then it is best for a plumber to do the job for you instead. You should also hire a plumber if you are concerned with the problem worsening or if you find another (related or unrelated) plumbing problem while setting up the gasket.