Black Tank Valve/Discharge Under Coach Rather Than In A Bay?

With rare exception, I've always seen Class C's valves under the body, not in any compartment.

The main issues will be if you're dragging or plowing the rear. In that case, you could damage the valves and pipes but it may be the only way to get out of the bogged down mess you'll be in.

Also as bobndot said, watch those parking curbs when backing.