What is a P-Trap and What Is It For?

P-traps are a type of plumbing fixture that is installed in the drainage system. It is used to prevent gases from entering the home from the sewer system by trapping them in water that flows into it through gravity or suction action. It is important to have it fixed or maintained regularly by professional plumbers to ensure it works well all the time.

A P-trap has two openings, one at the top and one at the bottom. The opening on top of the P-trap is called an “upper inlet” or “inlet” and it connects to a vertical drain pipe. The opening on the bottom of the p-trap is called a “lower outlet” or “outlet” and it connects to a horizontal drain pipe that goes outside.

The lower outlet opening should be located below where any water will splash out when you are washing dishes, taking showers, etc. Here’s what you should know more about P-traps.

More Facts About P-Traps 

As mentioned, a P-trap is a plumbing fixture that helps create an airtight seal that prevents sewer gas from entering your home. It is available in different materials, such as polypropylene, ABS, PVC, or brass. 

While metal is usually considered more durable, plastic lasts longer. Metal P-traps tend to corrode quickly. But if you still prefer a P-trap that is not plastic, you can get a brass one as it can also last for a long time. 

P-traps also vary in size. For example, bathroom traps usually measure around 1.25 inches in diameter while kitchen traps measure about 1.5 inches in diameter. With every use, water is flushed through the trap and replaced with fresh water. Solids and debris will stick to the trap over time, which will lead to the formation of clogs and should be replaced immediately. 

Clogs also occur on P-traps. For example, if you notice that your bathroom sink drain is draining unusually slowly, it could be because of loose hair clogged around the stopper below the drain. In this case, it can be removed using a long wire hook. 

For deeper clogs, you might need a plunger or a plumbing snake to retrieve small items that accidentally fell inside the P-trap or get rid of the clog. You might have to remove and reinstall the P-trap to remove the clogs or retrieve something. 

Common P-Trap Problems and How to Solve Them 

There are two common P-trap problems every homeowner should be aware of. These are: 

Dry P-Traps 

Evaporation causes a P-trap to dry up. But there could be other reasons why P-traps dry, such as a leak, dry winter winds, or a clog absorbing the water. Once the P-trap dries, you will notice a bad sewer gas smell wafting into your home. 

In this case, you should run a gallon or two of water down every drain every three weeks. You should do this, especially during winter when P-traps dry up faster. 


This is a common plumbing problem in general. Because of the P-trap bends, it is too easy for foreign objects to get stuck in the curve and cause clogs and blockages. It could be because of objects that should not be there in the first place, such as paper towels, hair, or wet wipes. 

When this happens, you can remove the clogging using a drain snake. For severe clogging problems, you have to remove the P-trap attached from its neighboring pipes and clean it thoroughly. But if clogs are a regular thing, you might want to consider getting your drains and pipes professionally cleaned by a trusted plumbing service in Spring Hill, TN


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