So you used the water at the campground/campsite? How was the water pressure, maybe there wasn't enough pressure to get things working. Another maybe silly question. If you use a water pressure regulator attached to spigot, assuming you changed out you fresh water line for another hose dedicated for black tank is it possible you didn't detach water regulator causing low water pressure preventing black flush to function properly?
05 Ram 3500 Cummins Dually
14 8280WS Rockwood Sig. Ultra Lite
Prodigy 3 brake Controller
TST 507 TPMS
2017 = 30 nights / 2018 = 7 nights