What is the purpose of a P-trap?

bathroom p-trap

Have you looked under your sink only to see a myriad of pipes? You know water needs to drain from sink but is all this plumbing pipe really necessary? Yes! More than just for water, those pipes help keep your home safe and smelling clean.

What is a P-trap?

In most Sacramento homes, there is a P-trap installed under the sinks in the bathroom and kitchens. A P-trap is a plumbing fixture that has several purposes. It traps debris that has drained from the sink and prevents it from forming a clog deep within the plumbing system, and to stops sewer gases from passing into the home. P-traps can be made from PVC pipe or steel, the latter is often used for exposed plumbing as it looks more attractive. While there are other styles of traps available, it is important to also know which are prohibited by the California Code from use.

How the P-Trap Design Works

A P-trap gets its name because it combines two 90 degree joints with a horizontal overflow pipe and gives the entire unit the shape of the letter “P.” One of the 90 degree joints exits the drain of the sink and then is joined to another which contains a water seal system that allows for water to flow into the overflow pipe, but not to flow backward toward the sink.

It is this back flow prevention that prevents sewer gas from escaping into the house. Sewer gas can contain many noxious odors which at the least, may smell like rotten eggs and at their worst, can be explosive and poisonous. The traps installed in the plumbing lines help to form a barrier of water within the P-trap. At the bottom of the “P” is a small cleanout tap that can be used to remove clogs the P-trap has contained.

P-trap Installation

One of the best aspects of the P-trap is that is inexpensive and easy to install. For our DIYers, be sure to correctly join PVC pipe to ensure tight seals and avoid leaks. California code does state that there are certain restrictions and cautions on using this style of trap that you should know. Our Sacramento plumbing team can help you determine whether the P-trap is allowed on the plumbing section you wish to install it but there are two rules of thumb to keep you on the right side of the code. 

  1. First, you may not install more than three utility appliances onto one P-trap. This means if you have multiple sinks in a wash room, for instance, only three sinks can be attached to a line using one P-trap.
  2. The second rule is that any P-trap that is installed on a plumbing line that will infrequently be used should have a trap primer applied. A trap primer helps to keep the seal in place that will prevent the passage of sewer gas. In frequently used P-traps or ones in very dry climates risk having the water evaporate within that is necessary for the trap to work. 

So, if kitchen or bath upgrades are on your ‘to-do’ list or you have mysterious smells coming from your pipes, remember the P-trap. When in doubt, call our professional Sacramento plumbers team to to give you a hand.