Winterizing on a Hill (or with RV parked on an incline)

When you blow out the lines on a level RV, the air pushes the water uphill and out of the faucets.
Your water lines are not level. So no, the RV does not have to be level to winterize.
I use the blow out method to winterize.

If you are going to run the refrigerator while in storage, then it should be fairly level to avoid damage to the refrigerator.