If I must use the dump station after a holiday weekend I expect to spend quite a bit of time in line. Ditto for getting gas at a convenience store - the person ahead of me will leave their car at the pump, go inside, and do a weeks worth of shopping while everyone else waits, then get in their car and use their cell phone.
I have a 12V marine pump and plastic barrel in the truck bed. The gray water gets transferred to the barrel & dumped via gravity at the dump station at my convenience, usually the day before we and everyone else breaks camp. The black tank gets emptied at home down the sewer cleanout and the tanks are rinsed when I get around to it.