True or False: Sink traps must be filled with water during air testing.

Sink traps must indeed be filled with water during air testing to ensure that they function properly during the test. The purpose of the sink trap is to create a seal that prevents air from entering or escaping through the plumbing system. If the trap is dry, it can allow air to flow freely, leading to inaccurate test results regarding the building's airtightness.

Therefore, for effective airtightness testing, it is crucial that the water remains in the trap to maintain the integrity of this seal. This practice holds true for all types of buildings, regardless of size or the season in which the testing occurs.