My rig has two black tanks, the front one came with a factory flush system, and I had a tornado flush system installed in the back tank. They make rinsing the black tank a breeze, help keep your tank level indicators clean and working properly, and help to eliminate unwanted odors. However, as good as they are, after I've flushed for a couple of minutes, I usually close the dump valve and let the tank fill about 2/3 full and then dump again. (Caution: make sure to closely watch the tank level when doing this, if not you will end up with water in places you don't want it.)
My gray and galley tanks don't have tornado flushers, but we do re-fill and rinse them after dumping, and keep them treated. The gray tanks will really stink the camper up more so than the black tanks if they aren't kept up properly. Most people do a good job maintaining their black tanks, but don't do anything special with their gray tanks and can't figure out why the trailer stinks.
Mike in Tennessee
Former 2 time FR owner
2007 Crossroads Cruiser 30QB Fifth Wheel
2008 F-250 Lariat 4x4 6.4 Powerstroke
Firestone Ride-Rites w/cab control