Sink Trap Leaking? Here is Why and How to Fix it Fast

Why Does My P-trap Keep Leaking?

A leaking sink trap is not as bad as a leaking water pipe, but it is a problem you want to fix as soon as possible lest it damages your sink cabinet and floor. But why would a sink P-trap leak every time you are using the sink?

A leaking sink P-trap is a sign that the connections are loose, it is not properly installed, it is not well aligned with the pipes, the compression washer is faulty, or the connections are cross-threaded. A crack on the P-trap can also cause it to leak.

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If a brand-new P-trap is leaking, it was definitely not properly installed. Make sure that the compression washers are not upside down, the long leg of the trap is connected to the tailpiece, and that the trap is properly aligned to the drainpipe.

To fix a leaking sink trap, make sure that it is properly aligned with the drainpipe, and that the connections are not cross-threaded. If you have a plastic P-trap hand tight the connections, or use slip-joint pliers to tighten a metallic one. You may also need to remove and reinstall it properly. A cracked P-trap will need to be replaced.

A P-trap has 2 main functions:

  • It holds a little amount of water at all times which acts as a barrier preventing sewer gases from coming up through your sink drain. Anytime you have a sewage smell in your bathroom or kitchen, it is a good sign that the trap is empty.
  • Its shape allows it to trap potential drain clogs, preventing them from clogging the drainpipe farther away. It is easier to unclog a P-trap than a clog many feet away from the sink drain.

A professional plumber will charge you between $100 and $200 to fix a leaking sink trap, while it will cost you not more than 20 minutes of your time if you fix it for yourself. If you have to replace the P-trap, a new one costs under $20.

How to Troubleshoot a Leaking Sink Trap

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Duck under the sink and inspect the overall condition of the P-trap and drainpipe connections. Check if you can spot the exact area the P-trap is leaking from.

If the leak is not clearly visible, plug off the sink drain and fill it with water. Remove the sink stopper and watch the connections under the sink as it drains. Focus on the connections and you will spot the faulty one.

The next thing you need to look at is how the P-trap is installed. A P-trap has a long leg and a short leg. If the trap is correctly installed, the long leg should be the one connected to the tailpiece (vertical pipe from the sink drain opening) while the short leg is connected to the drainpipe.

Once you have established that the P-trap is properly installed, the next thing you need to look at is the status of the connections. Are the couplings/compression nuts loose or cross-threaded?

A cross-thread refers to a situation where the threads on the female connection and those on the male connection are crossed due to poor alignment. When that is the case, the connection will leak and if the connection is tightened forcefully the threads will be stripped.

If you are dealing with a loose connection, the solution is always easy. Just tighten the connection with your bare heads or slip-joint pliers and your problem is fixed.

P-trap connections loosen due to the constant expansion and contraction as you pour hot and cold fluids in the drainpipe. With a loose connection and water draining first (pushing the P-trap down), the trap pulls away from the drainpipe and tailpiece, and water starts dripping from the connections.

How to Fix a Leaky Sink Trap

The method to use to fix a leaking sink trap will depend on what is causing the leak in the first place. Here are the 3 main methods of fixing a leaking sink p-trap:

1. Tighten the Connections

If you have discovered that a loose connection is the source of the leak in your sink trap then fixing it will take a minute.

Since most P-traps are made of plastic, their connections are meant to be hand tight. To properly tighten a P-trap connection, grab the tailpiece or drainpipe with one hand and turn the compression nut clockwise with your other hand.

If your lack the physical ability to turn the compression nut until it’s properly tight, grab a pair of slip-joint pliers which are also known as Channellock and give the nut a ¼ turn clockwise.

For a metal P-trap, turn the compression nut clockwise until snug. Grab a pair of slip-joint pliers and give it a ½ turn clockwise or more. Be careful however as overtightening the connection can strip the threads.

2. Remove and Reinstall the P-trap

If the drainpipe and P-trap connections are offset, the connections are cross-threaded or you suspect that compression washers are faulty, you will need to remove then reinstall the P-trap properly.

A compression washer, also known as a slip washer is a plastic or rubber ring with a tapered end, which sits at the top of the female connection. When you tighten the compression nut/coupling, the washer is compressed between the 2 connections creating a watertight seal.

If the washer is installed upside down, it is broken or has shifted, you are bound to have a leak in your P-trap. Some P-traps connections however do not have a compression washer, as it is usually integrated with the male connection.

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  • Clear the area under the sink. If you use the area under the kitchen/bathroom sink to store stuff, clear it first to get sufficient working space.
  • Place a bucket or bowl under the P-trap. The P-trap is always full of water and gunk, and you do not want to mess your floor with them.
  • Loosen the connections. Once again, seeing that the connections are usually hand tight, attempt loosening them with your bare hands first before reaching for the Channellock.
  • Once the connections are loose, gently pull the P-trap down and empty the water in the bowl. Clean it if is dirty.
  • Check the condition of the compression washers. If they upside down you will only need to change their orientation but if they are broken, they will need to be replaced.
  • Reinstall the P-trap. Push the compression nuts in the trap and drainpipe male connections followed by the washers. Attach the P-trap to the tailpiece and drainpipe and tighten both connections until snug.

Pro Tip: A common mistake people do is tighten one connection before even attaching the other. To get good alignment and therefore a watertight seal you need to tighten the 2 connections alternatingly.

You also do not need to use plumber putty or any type of tape to get a good seal. A properly installed P-trap will never leak and hence does not need any form of sealant.

Once the installation is complete, plug off the sink drain and turn on the water until the sink is full. Remove the stopper and check for leaks around the P-trap connections.

If you get any leaks tighten the connections ¼ turn with a slip-joint pliers and check again. If you did everything right your P-trap will not leak again.

3. Replace the P-trap

If the P-trap, compression nuts, washers or a combination of parts are cracked/broken, the best and long-term solution is to replace the trap. Take your old P-trap to the nearest home improvement store and buy a matching replacement.

Alternatively you can order one online. While sink traps are usually universal, you will need to measure your drain opening and order either a 1 ½ inch or a 1 ¼ inch trap. A new P-trap will come with the compression nuts to install them, and washers if not already integrated to the male connection.

If you would like to learn more on how to fix a leaking kitchen sink then check out this post.

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