Thanks for the quick helpful replies.
The black tank is trashed. Must have bottomed out a few times, broken up in several places and will need replacing. However, I already have a nice composting toliet, so I will likely seal off the opening to the black tank and go without one.
The grey tank is intact, but the connector going from the grey to the black tank is missing. There is hole where the flange is on the grey side, it appears broken off. I need to crawl under there again and see how bad it is - hopefully it's just the coupling and that can be replaced. I can just drain the grey directly and bypass the missing black.
Before I even attempt to hook up the water, I need to check all the plumbing for leaks. There appears to be minor water damage under the hot water heater, which is no surprise. Also the lavatory faucet appears to leak at the base. I will probably swap that out entirely and put in a different sink and vanity top. I also want to open up some easier access to the fresh water tank, which is concealed below my dinette couch and the lid screwed shut.
I haven't tracked down the water pump yet, but I want to check that also. I will likely just bypass the hot water heater if necessary. I can live without it.
Everything original that I remove will be cleaned and put into dry storage. I figure the bits and parts might come in handy at a swap meet. The original gas stove and fridge were removed long ago by a previous owner. So, I am going to go ahead and lose the gas furnance (I live and camp in south Florida) to free up space and make the entire camper propane free (going with solar eventually). The gas furnace is the only original appliance still remaining.
I am new to owning an RV or camper, so I have a ton of stupid redundant questions, and I have scanned and selectively read all 36 pages of the Repairs forum archive here. Thankfully, my camper was in pretty good shape to start with, and had no major flaws other than the previous owner stripping out most of the propane system.
I am also new to deep cycle batteries and 12-volt systems. I will not be making any long road trips in the camper any time real soon and want to get everything up to speed before hitting the highways.