Not trying to be difficult here, but how do you fill your black tank multiple times at the dump station?
Typically our stations have the dump section and farther down is the fresh water fill. If I am coming home from a weekend, my fresh tank is almost empty while the gray tank is full and black is less than half. I usually empty the rest of the fresh into the black tank while waiting in the dump cue. Once pulled up, I dump the black followed by the gray to rinse out the hose. They do have an outside wash down hose on a 30s timer, but it is not long enough to reach inside. If I were to go to the fresh supply and refill, I would need to loop back around to the dump cue to do it all over again. Many times this is not practical since it is at a rest stop with one-way routes and would require you get back on the freeway, turn around and return to the rest stop again.