How To Fix A Leaking Sink P Trap

The first signs of a leaky P trap under a bathroom or kitchen sink might be a small pool of water growing on the floor. This is wastewater leaking, so the issue needs to be solved quickly to prevent it from contaminating your home.

If the leak is left too long, you might start to get some strong sewage smells in and around your sink.

Here’s how to fix a leaking P trap.

What is a P Trap?

Before you can learn how to fix a P trap, you have to understand exactly what it is. If you look in the cabinets under your sink, you’ll see that curved, U-shaped pipe going directly down from the bottom of your sink.

While at first glance this pipe looks like a U, if you tilt your head or turn the pipe on its end, you’ll notice the P. That’s why this pipe is known as a P trap.

In plumbing systems, wastewater and the substances within them go down the drain and into a sewage system.

However, since water is not constantly running through these pipes, they can dry out, allowing the waste to decompose and rot. Through this process, gases form, creating a smell we associate with sewage, which can also be dangerous in large exposures.

The entire purpose of a P trap in your sink piping is to block sewage gases from wafting up your pipes, through your drain, and into your home.

Gases want to escape the pipe by going up or down, but they get “trapped” in the curve of this P pipe. Toilets, sinks, showers, and other drains are all connected to a P pipe. It might be valuable to know how to fix a P trap since your home has so many of them!

What Are Causes Of A Leaking Sink P Trap?

Improper Installation

While it might not look complicated, installing a P trap correctly to prevent leaks can be a bit more involved than you might anticipate. Internal washers must be used to prevent leakage. They must be installed with the beveled edge facing the correct direction and the pipes must be measured to fit correctly.

A P trap is likely to keep leaking if it is installed without an important piece to the P trap puzzle, or with a piece facing the wrong direction.


Some pipes or compression nut materials are more susceptible to corrosion than others. Additionally, the speed at which a P trap or its collection of important pieces can corrode depends on the corrosivity index in the draining water, corrosivity of waste poured down the drains, and the thickness of the plumbing material.

A thin-walled P trap pipe or an improperly fitted compression nut is likely to invite corrosion, leading to a leak.

Over-Tightened Trap Compression Nut

While this might fall into the “Improper Installation” category, over-tightened compression nuts are specific enough to deserve their own category. One of the most common causes of a P trap leak is over-tightening a “lock nut.”

Drain trap manufacturers specifically warn against over-tightening, since this can cause the materials to crack. Even a metal trap compression nut can crack if it has been over tightened.

Improper Fit

If your pipes are too big or too small for the washers and compression nuts used, then a leak will likely occur. Even if a leak doesn’t happen right away, eventually the misfit pieces will loosen, crack, or corrode and cause a leak.

Deteriorated Washers

Rubber washers might lead to a leak since rubber hardens and dries out over time. If your P trap’s washers are hard or deteriorated, or if the washers have become misaligned over time, then they’ll need to be replaced or realigned. 

How Do You Fix a Leaking P Trap?

For many P traps, they’re easily accessible under your bathroom or kitchen sink. For others, like showers or bathtubs, they’re hard to get to without some serious demolition. Always consult a professional before taking on any serious plumbing maintenance so you don’t end up doing more damage than good.

If you have a leak under your sink and it’s easily accessible, however, try to figure out where it’s coming from. When figuring out how to fix a leaking P trap under the sink, you might be able to see the issue.

If you can tell that it’s coming from one of the compression nuts, check to see if your nut is cracked or loose. If it’s loose, place a bucket under your P trap and then give the nut a small tighten.

For a metal trap, hand-tighten it and then give it half a turn with slip-joint pliers. For a plastic trap, hand-tighten the nut and then give it a quarter of a turn with slip-joint pliers.

If your P trap is still leaking after this, then you likely have a deeper issue with fit, corrosion, or a misplaced washer, and the entire trap may need to be removed.

Anything that’s corroded or cracked will need to be replaced, including washers, pipes, or nuts. If you’re not 100% confident in how to fix a leaking P trap, you can take the entire piece to your local hardware store for appropriate replacements.

Need Help With a Leaky P Trap?

Sink issues can throw a wrench in the harmony of your home. Unattended issues can also lead to larger problems and more disruption.

The best way how to fix a leaking p trap under the sink is to address it quickly. Stop issues immediately with the expert team at John C. Flood. For sink repairs, call the local plumbing experts at John C. Flood at (703) 214-5611 or contact us online.

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