[DQDick]

I hope I'm wrong, but the way you wrote the question leads me to wonder if you are sitting parked with the black tank valve open. If so, you have the dreaded pyramid of poop. You can leave the grey tanks open, but the black tank must stay shut until you are ready to leave or it is full. If you leave the black tank open the liquids drain out and the solids and paper stay and begin to pile up and harden. If that's what's happened you'll have to clean and flush your tank out. Again, if that's what is wrong, I've never dealt with it but some others here have and will be along with advise on where to go from here.