What is a P Trap and What is it Used For?

If your drain directly flushes your waste down into your sewer line, why don’t you normally smell sewage? Well, you have your sink’s P-trap to thank for that!

What Is a P-Trap?

The U-shaped PVC or stainless steel pipe under your sink traps a small amount of water which mainly prevents sewer gas from entering your home. But this is one of the many benefits and uses which come with having a functioning P-Trap.

What is the Purpose of a P-Trap?

Stopping Sewer Gases

It goes without saying that sewage smells, and that’s because it’s full of gases that not only stink, but are harmful to you at high levels, including methane, hydrogen sulfide, nitrogen oxides, sulfur dioxide, ammonia, and more. Continual exposure to these fumes can cause health problems including:

  • Headaches
  • Fatigue
  • Irritability
  • Appetite loss
  • Memory issues
  • Light-headedness
  • Sinus infections
  • Bronchitis
  • Pneumonia

You’ll likely notice the smell of rotten eggs coming from your sink, meaning these gases are making their way past your P-trap and into your home.

Preventing Clogs

The U-shape of its piping makes it so your P-trap will likely clog first before your drain line. It’ll normally catch the debris, allowing you to toss the waste elsewhere by removing the trap and clearing it out by hand – much more manageable than your typical drain line clog.

Protecting Your Valuables

It’s pretty common to lose small jewelry like your ring or earrings down your drain. You may have thought your valuables to be forever flushed through your local sewer system, never to be seen again, but it’s likely been sitting at the bottom of your U-bend all along. Taking the time to remove your trap and clear it out is plenty cheaper than buying new jewelry.

Issues You Might Face

Evaporated P-Traps

Whether you’re in a dry climate or haven’t used your sink in a while, the water which is supposed to sit at the bottom of your P-trap will eventually evaporate, no longer trapping the sewer gases from entering your home. One solution is to use a tap seal primer, which adds water to your P-trap as needed to maintain its function.


Instead of evaporating, the water in your P-trap could be draining because of a leak. If you notice drippage or damp spots underneath your sink, it looks like you’ve got yourself a leak in your U-bend. Consult your trusted professional plumber for servicing the leak.

Insufficient Ventilation

If your drain line doesn’t have proper ventilation, the air suction pushing and pulling throughout your lines as you drain your wastewater will empty the water in other P-traps besides the one you are using at that moment, leaving your home potentially vulnerable to sewer gases in multiple drains at the same time.

P-Trap Cleanout

There are a few homemade drain cleaning remedies you can use on a regular basis to keep your U-bend in good shape and less likely to cause you problems.

Boiling Water

Boiling water is a great way to soften and flush out scum build-up from the likes of soap and grease along the walls of your piping.

  1. Boil a pot of water.
  2. Slowly pour it down your drain, a little at a time.
  3. Wait about 5 minutes.
  4. Run cold water to congeal any remaining grease.

Baking Soda and Vinegar

Baking soda and vinegar are a great addition to your boiling water if you need a more thorough drain clearing and cleaning solution.

  1. Prepare 1 cup baking soda, 1 cup vinegar (any will work, including white vinegar).
  2. With both of your cups of baking soda and vinegar ready at hand, pour half a cup of baking soda down your drain.
  3. Next, slowly pour half of your cup of vinegar into the drain. You should start to hear fizzing – the chemical reaction between your baking soda and vinegar.
  4. Let it fizz and stand for a few hours.
  5. Pour boiling water down your drain to give it a good clean flush.

Baking Soda and Salt

Another quick home remedy clearing and cleaning your drain is salt and baking soda.

  1. Mix half a cup of salt and half a cup of baking soda together and pour it down your drain.
  2. Let it sit for at least 30 minutes.
  3. Finally, prepare boiling water and pour it slowly down your drain to clear away your solution.

Wire Brush

If your favorite homemade cleaner isn’t doing the trick, then you may need to go straight to scrubbing and cleaning out your U-bend directly.

  1. Make room under your sink, clearing and relocating anything that might get in your way.
  2. Place a bucket under your piping to catch any dripping or spillage.
  3. Loosen the two coupling nuts connecting your trap to the drain and overflow pipes, and set them aside.
  4. Clean out the inside of your trap with a wire brush.
  5. Reassemble your p-trap, make sure that your washers are set properly, and the coupling nuts are re-tightened.
  6. Finally, run your water for at least 30 seconds to ensure there’s no leakage.

P-Trap Installation

There are two general rules to installing a P-trap you should consider, especially in states like California which have codes that involve restrictions for using this kind of a trap.

  1. Don’t install more than 3 appliances all on one P-trap or you’ll overload it.
  2. Any P-trap that won’t be frequently used should have a trap primer attached to it. It’ll keep your seal and prevent sewer gases from passing through and easily entering into your home. This is also a good consideration for those extra dry climates which will quickly evaporate the water in your trap.

Find Fast Resolutions at Deer Valley Plumbing

Sometimes your DIY, homemade drain cleaning and clearing solutions aren’t enough to fix your problem, and you might be facing a leaking P-trap. At Deer Valley Plumbing, we offer emergency services and same-day scheduling so that we can clear those clogs, stop those leaks, and get those pipes freely flowing again. Call us at 602-832-8418 and schedule your next service with us today!

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We understand that plumbing problems can cause a major disturbance to your daily routine. When an issue arises, you need a fast, cost-effective solution. Our team is trained to handle any problem you are facing. We are equipped with the knowledge, skills, and tools to perform the service you need when you need it.

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