Drum Trap

A drum trap is a cylindrical metal trap — roughly the size and shape of a large tin can — that was used under bathtubs, floor drains, and laundry tubs from the early 1900s through the 1950s. Like all traps, it holds a water seal to block sewer gas. Unlike a P-trap (which self-cleans as water flows through), a drum trap collects debris at the bottom and requires periodic manual cleaning. Modern plumbing codes prohibit new drum trap installations, but millions remain in older homes.

Why drum traps were used

Before flexible drain pipes became common, drum traps offered a large water seal that was easy to make watertight with lead and oakum in the era's cast iron construction. The large barrel capacity was thought to create a reliable seal. The top cleanout cap allowed access for cleaning — an advantage over the buried P-traps of the era.

Why drum traps are now prohibited

The IPC and UPC prohibit drum traps in new installations for several reasons:

• They trap debris and require regular cleanout to prevent blockage
• The horizontal inlet and outlet at the same level means any solids not trapped in the drum go directly into the drain — the trap doesn't self-clean under normal flow
• Drum traps are difficult to service — typically buried in the floor with only a threaded cleanout cap accessible
• Siphoning can remove the water seal more easily than in a P-trap

When you find a drum trap

In a home with original 1920s–1950s plumbing, the bathtub drain may connect to a drum trap buried in the floor (often under the bathroom tiles). A plumber can access it via the cleanout cap to clear clogs. If the bathtub drain is chronically slow and snaking doesn't help, the drum trap may be packed with debris and require replacement — a more involved project requiring floor access and typically replacement with a modern P-trap.