RV holding tanks come in many different sizes & shapes and can have the outlet on an end, bottom or side so cleaning results can vary. Our in-tank flusher is directly below the toilet and cleans the tank well there but doesn't reach the sensors and they never work properly. With some tanks, a backflush elbow works well (and sometimes not) and could be used to supplement the built-in flusher. We have a backflush elbow from a previous TT and it doesn't work for our current TT.
Should have a hose dedicated just for the tank flusher and should be a different color (ours is grey) so the wrong one doesn't get used.
It can help to fill the tank as full as you can before you open the valve so you get a good surge and flow of solids. Emptying the black tank is one of the first things I do when breaking camp then I hook up the flusher and let it run for say 15 minutes then look down the toilet to see if the tank bottom is clean. I installed a valve behind the toilet so I can shut the water off and see the tank bottom easily. If the tank bottom isn't clean I repeat the process again. Filling up the tank is slooow tho. Sometimes I'll use the shower head to get water in faster (I take the head right off the hose).