Trap

Waste Trap

In plumbing, a trap is a U-, S-, or J-shaped pipe located below or within a plumbing fixture. An S-shaped trap is also known as the S-bend but became known as the U-bend following the introduction of the U-shaped trap. The new U-bend could not jam, so, unlike the S-bend, it did not need an overflow. The bend is used to prevent sewer gases from entering buildings.

WIKIPEDIA ENTRY FOR TRAP.

Trap Picture   Trap 2 Picture