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Adventures in Plumbing: When a Trap Dries Out

One of the urinals at work has been out of order so long that the water in the trap evaporated. I noticed because I could suddenly hear the hollow sound of distant flushing and water rushing down a pipe. For a few days, I was fascinated by the acoustics, but the novelty wore off, so I filled the trap back up with water. The sound-deadening properties of a couple inches of water are amazing. I thought it was odd that I never smelled any sewer gas, but I’m now thinking that air only rushes into the stack and never out.