[08quadram]

I live in iowa and have used compressed air to blow out my lines for years. Never had an issue. Open the low Point drains and let the system drain out to the greatest extent possible. Close the valves pressurize the system with the city water connection and then start working your way to the back making sure everything is blown completely out. Didn't reopen those low Point drains to get the residue. Same procedure local municipalities use here to blow out all the campground bath houses and park shelters with water when they are ready for the winter.

I use antifreeze and all the traps, a couple inches in the toilet, and then I pour the rest down into the black tank. I also usually let the pump run for about 30 seconds to make sure there isn't any water in the pump.