instruction manual

I just bought a 1983 Aluma-lite and I have no idea how anything works. Oh I know how to work the stove, sink and fridge (had to replace that) but I can't figure out how to work the heaters, water heater or water pump. From what I can tell there is no way to drain the fresh water tank and the black tank won't empty even when I pull the handle outside. The grey tank empties though.