Well Silver,
The "Black Pyramid" is a well known issue and is the direct result of not using enough water in the flush. If there is enough in the black tank, solids will simply roll off.
Your tank level gage may just be jammed on the solids.
Now, what you have to do is plan to go to some where that you can dump, go get a bag of ice, fill the tank with as full as you dare water or what all, get unhooked (if required), then dump in the ice and drive to the dump the long way.
Rinse the tank at least once while you are at the dump.
Matt
