Sometimes you may not have another chance to dump for a long time. The last time I dumped at a campground on Friday of memorial day weekend, from there I stayed in the parking lot of a Camping World parking lot with electric but no dump area, I arrived in NY last Tuesday morning and parked in the driveway of a house I am clearing out and selling. The house has been winterized, water turned off house toilets not useable with electric hookup available. I will be here for at least another week, if I came here 1/2 full I would be in trouble soon.
If you are worried that a near empty black tank will not dump properly just fill it up with water