What Is a Trap?
A trap is a curved or chambered section of drainpipe that holds water and blocks sewer gases from entering a bathroom. The water seal also helps keep odors and pests out of the room. Traps sit below sinks, toilets, showers, and tubs, where wastewater flows through them before reaching the drain line.
Quick Facts About Trap
Category
Drain plumbing component
Used for
Blocking sewer gases
Common confusion
Often confused with a cleanout
Also called
Plumbing Trap, P-trap
Often discussed with
Bathroom Plumbing Repair
Key Takeaways About Trap
- Its water seal blocks sewer gases.
- A trap sits below or inside a fixture.
- A trap is not the same as a cleanout.
How Trap Works
A trap works by keeping a small amount of water in a curved section of drainpipe. Wastewater pushes through the curve, while the water stays behind after the fixture drains. That water seal blocks gases from traveling back through the drain.
Related glossary terms: Trap Primer, Cleanout, Siphon.
A sink usually has a visible P-trap below the basin. A shower or bathtub trap may sit below the floor, so you may not see it. Traps need a clear path for water, and a blocked trap can slow drainage or cause backups.
A dry trap can allow odors into the room. This can happen when a fixture sits unused for a long time or when a leak lets the water seal escape.
Expert Note
When we inspect a trap, we check the pipe connections, water seal, and drainage flow. We also look for leaks, corrosion, loose fittings, and signs of a blocked line. A trap below a shower or tub may require access through a nearby panel or finished surface.
Trap in Practice: A Real-World Example
During a bathroom plumbing repair, a slow sink may trace back to hair and buildup inside the trap. We can inspect the trap, protect the cabinet, and check the connections after clearing the obstruction.
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Related Terms
Trap Primer
A Trap Primer is a plumbing device that adds water to a drain trap when the…
Cleanout
A cleanout is an accessible opening in a drain or sewer pipe. Its removable cap lets…
Siphon
A siphon is a flow path that moves liquid from a higher level to a lower…
Grease Trap
A Grease Trap is a plumbing device that catches fats, oils, and grease before wastewater enters…
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