By your history, I see you have a new travel trailer. I would pay my local dealer to show me how to winterize properly. Each vehicle has its' own peculiarities. I would schedule a time when the dealer will allow you to accompany the tech when they actually do the work. We never use compressed air on the water lines. Maybe your brand of trailer recommends such? I would want a professional to teach me the correct way rather than just an OK guess that may or may not be correct. Frozen pipes and or damaged water heater is not good...Just saying. After being shown by our local dealer it takes us about 2 1/2 gallons to properly winterize each year; and about 1/2 to 1 hour to perform.