Our previous Class C had a "Low Point Drain" label on the kitchen cabinet they were located in. That was for the Hot and Cold plumbing. The coach we have now, has that label on the outside compartment where they are. Again, Hot and Cold. Then I'd expect to also drain the Fresh Water Tank and the Water Heater. Let the water drain out of the hoses for your Shower and Outdoor Shower.
If you're expecting a deep freeze, be sure you blow out the toilet flush valve, and pour the water out of (or RV antifreeze into) any traps you have. Typically Kitchen, Shower, and Lavatory.