Drum Trap
An older cylindrical trap, common under bathtubs in homes built before the 1970s, now outdated because it clogs easily and is hard to clean.
A drum trap is a squat cylindrical canister, larger than the pipe feeding it, once installed under bathtubs and sometimes lavatories in older homes. Instead of a simple bend, it holds water in a drum-shaped chamber with the inlet and outlet at different heights to maintain a seal. You typically find one with a screw-off cap on top, set into the floor or accessible from a basement below the tub.
Drum traps fell out of favor because the same shape that holds water also traps debris. Hair, soap, and sediment settle in the wide chamber and are hard to clear, so a drum trap clogs more readily than a P-trap and resists a standard snake, which tends to coil inside the drum rather than push through. Many also vent poorly by modern standards, leaving them prone to slow drainage and odor.
When a tub on a drum trap drains slowly or smells, cleaning means unscrewing the cap and clearing the chamber by hand, a messy job if the cap has corroded in place. Plumbers often recommend converting a drum trap to a modern P-trap when the bathroom is being reworked, since code no longer favors them and the recurring clogs rarely improve with snaking alone. Until then, the access cap is the maintenance point.
Talking to a contractor about this?
Run the project past a licensed plumbing pro first. Calls are answered around the clock and routed to a pro serving your area.
- Vent Stack / Plumbing Vent : The vertical pipe that runs up through the roof to let air into the drain system, so waste flows freely and trap seals are not siphoned away.
- Air Admittance Valve (AAV) : A one-way valve that lets air into a drain when needed but stays sealed otherwise, providing venting for a fixture without running a pipe to the roof.
- Branch Drain : A horizontal drain line that carries waste from one or more fixtures over to the main vertical stack, sitting between the fixture trap and the soil stack.
- Soil Stack : The main vertical drain pipe that collects waste from every fixture branch and carries it down to the sewer, extending up through the roof as the vent.