Which two parts of a trap are used to measure the depth of the trap seal?

• A. Inlet and outlet
• B. Crown weir and top of the dip
• C. Top lip and bottom
• D. Weir and baffle

Answer: (B)

The depth of a trap seal is determined by the height of the water column inside the trap, measured from the crown weir to the top of the dip. The crown weir is the highest point where water would spill over if the level rose, setting the upper boundary of the water surface. The top of the dip is the deepest interior point where water pools, forming the seal. The difference between these two points is the trap seal depth, which represents how much water is actually present to block sewer gases and resist siphon. The inlet and outlet describe where the trap connects to the piping system, not the water level inside the trap.