What I do is tend the filling and as soon as a drop comes out of the overflow tube(s) I jerk the hose out. The siphon doesn't get a chance to establish. Granted, if you haul this up, down and shake it, you will slosh more out, but I find that at most I lose a few gallons. I usually fill close to where I'm setting up so no big deal. I have been thinking about plumbing in some sort of antisiphon device, if one exists.
"I might be movin' to Montana soon..."
2013 Eagle 29.5RKS
2013 Ford 6.7L diesel F350