[scottz]

My plastic one did not have a check valve. A check valve would defeat the purpose of the vacuum breaker. As I understand it, when the vacuum breaker opens it introduces air into both legs (towards black tank and towards water inlet) allowing water to drain both directions. A check valve would prevent the water from draining out one leg. If nothing else, that would cause problems winterizing. When the vacuum breaker operates properly, there is no water remaining in the lines.