What Is a P-Trap?
A P-trap is the U-shaped section of drain pipe beneath a sink, tub, or shower. It holds a small amount of standing water that forms a seal, blocking sewer gases from entering the building through the drain. Every plumbing fixture connected to a drainage system requires one, and a trap that dries out stops working.
Why traps dry out
The water seal evaporates if a fixture goes unused for weeks, which is why a guest bathroom or a floor drain in a rarely used basement often smells. The fix is simply to run water into it.
Traps can also be siphoned dry by a drainage system with inadequate venting, which pulls the seal out when a nearby fixture discharges. That is a design or blockage problem rather than a disuse problem, and repeated drying in a fixture you use regularly points to a venting issue worth investigating.
The trap as an access point
P-traps under sinks are usually joined with hand-tightened slip nuts, which makes them the easiest access point in household plumbing. Removing and cleaning a trap resolves a large share of slow bathroom and kitchen sink drains, and it is the first thing to try before any chemical or mechanical intervention.
It is also where dropped jewellery ends up, which is the other reason people learn to remove one.
Frequently asked questions
Why does my drain smell like sewer gas?
Most often a dry P-trap in a fixture that has not been used for a while. Run water into it for thirty seconds and the seal reforms. If a regularly used fixture keeps smelling, the trap is being siphoned dry, which points to a venting problem worth having looked at.
Can I clean a P-trap myself?
Yes, and it is one of the more approachable plumbing jobs. Put a bucket underneath, unscrew the two slip nuts by hand or with slip-joint pliers, clean out the trap, and reassemble. Do not overtighten plastic nuts; hand-tight plus a small turn is enough.
See also
Related services
- Emergency Drain CleaningClearing of blocked sinks, tubs, showers, and toilets, including cable work and hydro jetting for stubborn or recurring blockages.
- Emergency Fixture Repair and InstallationRepair and replacement of faucets, shutoff valves, supply lines, garbage disposals, and other fixtures, including failed connections that leak.