We use or have used several different ones. The little packets are convenient but we have liquid on board too Camco, probably.
Our tanks black and gray are flushed when we dump before pulling out. Fill tanks to capacity, and empty the black first and let the flushing continue for five minutes, let water into the tank for five minuets or so so there is probably five gallons, in the black tank, of clean water.
Let the gray tank drain that is only soapy water and flush for a few minutes and close valve.
Driving down the road with a few gallons of water, in the tank insures there isn't any buildup anywhere.
We have put liquid soap in the black tank and water softener.
Then when we turn on the water through the flush system it all gets stirred around good before draining.
Through the opaque elbow, at the end of the, drain hose you can see the effect and quite a bit of foam.
That gets it about as clean, I suppose you can.
Just don't go with flushing the tank properly or sitting for a very long time with stuff in the tank.