What is a P-Trap? (with photos)

Various traps p.

Almost all household appliances that drain water have a siphon. Sinks, bathtubs, washing machines all have siphons to drain wastewater. A p trap is made up of a tailpiece, the curved trap piece and a drain elbow. The drain elbow for a siphon fits into the drain pipe that goes directly into the wall.

Codes require an s-trap (or s-trap) anywhere there is an open drain line that flows into the drain-sewer-vent system. As the name implies, the drainage-waste-ventilation system removes solid, liquid or gaseous waste from the house through drains and vents. For example, as water leaves a sink, it passes through the siphon, into the drain line, and into the sewer system.

P-trap under the bathroom sink.

The important thing about the p-trap is that it has a water seal along the curve of the trap. The seal prevents air or harmful gases from backflowing from the sewer line, but the original residue can still exit into the sewer system. If the gases could come back into the house, they would not only smell bad, but could cause illness and even explode.

A p trap can be made of metal or plastic. While metal is generally considered to be more durable, the reality is that plastic will last longer. While metal traps may look prettier, they corrode quickly. A grip on the curve, even with your fingers, and if it sags – even slightly – it needs to be replaced. There is one exception to this rule: large-caliber brass traps last a long time.

Depending on where the trap is located, it can vary in size. Bathroom traps are 1.25 inches (3.2 cm) in diameter. Kitchen traps are 3.8 cm in diameter.

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Each time the drain is used, the water is discharged through the siphon and fresh water replaces the old one. Solids will begin to adhere to the trap over time; consequently, obstructions will occur. In these cases, it’s probably time to replace the trap. A beginner can replace the p-trap in about an hour; however, an expert can do the same job in about twenty minutes. In some cases, a siphon that has a cleaning plug can be cleaned without removing and installing a new one – simply rinse water through the plug and remove debris with a drill or other tool.

It is important to know the specific plumbing codes for a particular country before removing or installing a new siphon. For example, in the United States, white PVC plastic pipe, polyvinyl chloride is commonly used for drains. But in Canada, black ABS, acrylonitrile butadiene styrene, is used. Every country is different so proper research is required before diving into any plumbing project.

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