Black tank flush hose routing question

[fiddler63]

I have a 2012 coachmen Chaparaal 280RLS fifth wheel. I removed the access panel to get at the water heater bypass, and noticed something I don't understand. The water line leading away from the black tank flush connection, does not go directly to the black tank, but instead, runs away in another direction that leads up thru the floor. Another section comes out of the same place in the floor (some kind of return, maybe) and then makes it's way over to the tank. Can anyone tell me why those pipes disappear vertically in the floor instead of going directly to the thank?

Thanks

[ependydad]

I believe that they go to an anti-siphoning valve to keep black water from following back the hose. It's usually in a closet or cabinet in the bathroom.

[fiddler63]

Holy cow, ependydad, I think you're right. I haven't checked yet because the trailer isn't here, but the two pipes (hoses) in question are tie wrapped to the bathroom sink drain and run up into that area. I haven't looked in the bathroom floor vanity cabinet, but I'm willing to bet a buck that I'll see some kinda access panel or screws.

Thanks a million