Black Flush Anti-siphon Valve

Douggrainer - that’s what I thought before looking at the new brass anti siphon I purchased. Definitely an anti-siphon and not a check valve. The ‘in’ side has a plastic valve to prevent water from flowing backwards. The ‘out’ side, which flows directly to the black tank, is exposed to air except when water is flowing in. Makes sense as “anti-siphon” that when water not going in it let’s air in to the black side so it drains back into the tank and can’t be siphoned, unfortunately after the water has drained into black tank the black line is now exposed to air and becomes a vent. Seems like a poor design element on a black flush to me. Am I missing something??