It's fairly easy to blow out a water system for winterization. The air fitting adapter is necessary to attach an air hose to the water system inlet. Most water systems are pressurised to work in the mid 40s PSI. You must never exceed that pressure, and 25 - 35 PSI works well. Your volume of air needs to have enough CFM to maintain an open 3/8" line for short periods of time. This would require about 4 or 5 CFM, or about what a 2 hp oil less compressor delivers.

Drain the water tank, and then attach the air hose, fire up the compressor with a regulated pressure of about 30 PSI, and open each spigot one at a time until no fluid is presented. Add RV anti freeze to each drain trap and toilet and the fresh water tank.

This system is especaily handy when often using the LQ during freezing weather. It's faster and less expensive than flushing each time with antifreeze. However for the owners who winterize one time a year, unless you already have the compressor, it would not be cost effective.

For about ~$18-$20, you can purchase the adapters that suck anti freeze directly from the gal containers. Most water systems with hot water tank by passes, can be winterized with about 1 1/2 gals of fluid. In our area the fluid is ~$4-$6 per gal.

Most marinas and many RV dealers use air to purge the water systems. Once the equipment has been purchased, it's a fast and easy process.

Draining the water system, doesn't get all the water out of the low spots in the line. Some water will remain and it will freeze, possibly damaging the system 

So follow Gards suggestions above.