A quick history. I bought my Sovereign
in 2004 and have been working on it off and on for 5 years. I'm nearly done with all my work and will be using it for the first time on a campout in two weeks. Anyhow, the PO didn't use the black tank properly and it appears she left the valve open all of the time leaving a nice caked on "residue" on the bottom the tank. Any ideas how I can clean this out? Is there some kind of treatment I can use to liquify this residue?