1. empty the holding tanks.
2. empty the water tanks including the hot water tank. Turn the pump on for a second to get any water out. Also, flush the toilet
3. put a little air, with adaptor to the city fill. Yes it make a difference, more water comes out.
4. I only pour rv antifreeze in to the holding tanks through the toilet and sinks drains, usually a gallon take care of this, and a little in the toilet to keep it sealed. You don't want any smells from the holding tanks coming back into the camper. I used to put antifreeze in to the water system, but quit, it made the water taste weird even after flushing. I feel blowing out the water lines empties it out pretty good.
5. I use dryease or how ever it is spelled inside. My camper is 12 years old and I have not had any freezing issues.