[JRTJH]

sourdough,

The factory is notorious for installing the anti-siphon valve "backwards". I'd guess they do that almost as much as they put the black/gray tank decals on the wrong handles....

That said, your valve may have just been installed backwards, it'd build up pressure and when you removed the hose, it would "spit back at you".... The dealership probably just removed it, installed a "open loop" and called it a day... You're good to go, it won't cause a leak and probably is more "leak proof" than any anti-siphon valve would be. The only problem is that there's no "valve to stop leaking" if the black tank should start to "siphon" through that fitting and out the hose. Most who have removed their anti-siphon valve have started using a "garden hose anti-siphon valve" on the trailer wall hose fitting. You can find them at Lowe's in the lawn irrigation section.

Thinking about it, your dealer may have installed a new "wall fitting" on your trailer with an anti-siphon valve built in. It would be essentially the same thing as your city water connection. Who knows, with any certainty, what they may have done, but if it's worked for 4 years, I wouldn't worry about it now LOL