Great info. I get what you're saying and the last owner did live in it for some time. I think you're on to something with the garden hose since the drain cap has a garden hose connector in it and there was a pile of sludge behind the cap when I removed it. Not a pleasant experience. There is also an added steel pipe saddled onto the grey water side after the valve I haven't looked into yet. Maybe a way to flush out the downstream side of the valves.
They might have taken the pump but the wiring is still in the trailer disconnected. I still have to track down where it goes to. I connected it turned on the switch and blew a 20amp fuse so that tells me the pump is still there and locked up or the wires terminate in a dead short. Thanks for the input.