Our rig has low-point drains for the hot and the cold piping. There is a third valve nearby that is the fresh water tank drain.
After dumping black and grey water tanks, I open the low-point drains, prop open the hot water heater pressure relief valve, and open the fresh water drain. After they all quit dripping, I screw in one of those schrader valve-to-hose-bib adapters at the main water inlet. They are available at any camping supply store.
Then feed compressed air into the system being careful to not apply more than 60PSI. More water will come out of the low-point drains. When that stops, they are closed. Then I crack the hose bib connection to the electric valve for the ice maker and apply the compressed air again until only air is coming out of that joint, then re-tighten.
At that point I apply compressed air again while DW goes around and opens each water valve in the coach, one at a time. Sinks, shower, flush the toilet, washer/dryer, etc., leaving each valve open until only air is coming out.
Then I pour antifreeze in each drain (sinks, shower, washer/dryer, toilet) to displace any residual water in the p-traps. Enough antifreeze combines with the p-trap water to prevent its freezing in the holding tanks.
All this sounds fussier than it really is and the real benefit is when you want to de-winterize, just hook up the fresh water hose to put water in your tank and go. Don't forget to make sure that the ice maker hose connection is tight and that the hot water heater fills up with water before you turn it on.
Dave & Cathy, 2002 Country Coach Affinity, 42', #6103, CAT C12, 2003 Cherokee Overland