".... the black tank developed this rock hard and large deposit...."
The dreaded POOP PYRAMID.
Gonna need to bust it up......awning rod, pole etc.
Then you need to fill tank full and dump
Then fill it about 1/2 full and dump in a bunch of digester and let sit for couple days
Digester then fill and dump again.
Then add 5 gallons of water and dump 10-20# of ice cubes into tank via toilet and immediately go for a drive over rough/curvy roads.
Fill and dump again.
Repeat until POOP PYRAMID is gone.
After you get rid of it...use more water!
Fill toilet bowl full when flushing poop
Don't dump tank until almost full (leave drain valve CLOSED until time to dump)
Flush/rinse after dumping
Add couple gallons back into tank so bottom stays wet and stuff doesn't stick
