You could also run a hose down the toilet while holding the valve open. I always carry a non-drinking-water garden hose used only for the "dirty work" and would use it to fill the black tank of I didn't have a tank flush. At least it would be faster than just standing on the pedal...
2014 Jay Flight 28 BHBE
2015 RAM 2500 6.4L HEMI, Tradesman 4x4, 3.73
Blue Ox SwayPro (BXW 1503)
Upgraded from an REI internal frame backpack and a Eureka 1/2 dome tent!