In a trap, the letter C best describes which feature?

• A. Vent
• B. Seal
• C. Drain
• D. Overflow

Answer: (B)

Traps are meant to hold a water barrier that blocks sewer gases from coming back into the building. The part of the trap that does this is the water in the bend—the water seal. This seal sits in the U- or P-shaped portion and creates a barrier so gases can’t travel up through the drain. It’s not the vent, which is a separate line for pressure relief; it’s not the drain, which is simply the passage for wastewater to leave; and it’s not the overflow, which is a fixture feature to prevent flooding. So the feature shown is best described as the Seal—the water barrier inside the trap.