camperdave wrote:
The vent is at the top of the tank, I don't see how it can siphon out. Maybe splash a bit out, but even then just re-route the vent to loop up a bit higher if it's a problem.
I'd be super leery of valving off the vent, even if only for travel.
Given the "standard" quality of most mfrs, it wouldn't surprise me at all if a bit of the overflow pipe/hose got stuck down into the tank a bit, which =would= siphon, once it got started. As a former farmer who used siphons from 1" to 4" in size, it's amazing how little head difference it can take to run a siphon.
Lyle