Super generalizations follow
Do you know if you had the winterizing kit installed? It would be a little 2 way valve down by where your water pump is, usually. You shoud see it and a little piece of tygon (clear) tubing attached to it. you usually just put that tube in your rv antifreeze and then go to each sink open the faucets and drain till pink. You should also bypass and empty your water heater. For your clean water tank just find the drain plug and drain it.
for black and grey just empty them.