So, just how "hazardous" can a tank full of poo be?

As for the fence post... what keeps the fence post door latched on the highway? I can tell when camping season begins here in Texas when I see people's poop tubes tumble tumble out of bumpers and other receptacles.

I just leave my hose in a plastic tub inside a storage compartment, so barring a hatch flying open, I don't really worry about a slinky escaping to play in traffic.