You might not have heard of an Anti-Siphon Trap Vent Device (ASTVD). It’s not the sort of feature that gets published on a sales brochure. Here’s what it looks like:

Anti-siphon vents are also called air admittance valves or cheater vents. I’ll either call it an “anti-siphon vent” (for short) or an air admittance valve (AAV).

Most RV owners notice their air admittance valves for the first time not with their eyes, but with their noses. When an anti-siphon vent goes bad, it allows sewer gases from your waste tank to escape into the living area. (This is usually when an RV owner realizes that a gray tank can stink just as badly as a black tank!)