Sundance 241BH - Black water tank fell out

I confess that a few years ago when I was either distracted or not thinking clearly, I was running the black tank flusher with the drain valve closed, and didn't notice until water was running off the roof. The water was clear because the rig had just come out after winter. When the black tank is empty, I always use the flusher to add a few gallons of water. I learned to not let my mind wander when doing this. Considering the flow capability of the vent pipe compared to the flow of the flusher, there's no way the tank pressure could be more than what's caused by the height of the vent.