After I dump the black tank, I put water in the black by holding down the foot flush until the black tank reads 1/3 full.
This accomplishes a couple things.
One, I never have dry anything in my tank. Paper or solids always have water working on them to break them down.
Two, I have never had a pyramid of paper or poop in my tank.
Three, my tank meters have never gone to the stuck on an incorrect reading situation that is common to some because TP got hung up on an sensor inside the tank and is conducting electricity through it.
My old TT had 30 gallon gray and black tanks and I never filled the black unless I was camping for over 10 days (3 of us camping usually, occasionally 4). Gray alway filled first and I would use a tote to dump it and the black would last generally until we left. I think one time I had to dump some black into it, top off with gray water and go dump give us a couple days worth of room on a 14 day camping trip.
So my point is, be generous with the water, Don't be afraid of starting off with a few inches or more to make sure everything gets broken down good. Then you can just fill the bowl to a normal level, do your business and flush without worrying about anything.
Lastly, if you put water in after dumping, it sloshes around on the way home and works on anything that is stubbornly sticking to the bottom or sides of your tank.