What component works to maintain the seal in a plumbing trap?

The correct answer is that a specific depth of water maintains the seal in a plumbing trap. In plumbing systems, traps are designed to prevent sewer gases from entering the living spaces while allowing wastewater to flow through. The critical component that achieves this function is the water held in the trap.

A plumbing trap retains a certain water level, forming a barrier that blocks the flow of gases. This water seal is usually a few inches deep, which effectively prevents odor from escaping while still permitting the passage of water and waste. If the depth of water in the trap drops below a certain level, the seal is broken, and unpleasant sewer gases can enter the building.

In contrast, the other options do not serve this specific sealing function. A float valve is used to regulate water levels in tanks or pools but does not directly maintain a seal in traps. A check valve allows fluid to flow in one direction but is not designed to hold water in a specific position like a trap. A pressure gauge measures the pressure in a system but has no involvement in maintaining a water seal in plumbing traps.