You can blow the waterlines out with an air compressor and hope you got it all or do it the right way.
I use a hand held, drill powered water pump like this,
http://www.amazon.com/Drill-Powered-Water-Pump-Garden/dp/B003EB6YHA. I hook the output up to the camper and the input is connected to a short hose dropped into a gallon of winterizer fluid. While I run the pump and assistant flushes the toilet until you see winterizer come out, then the shower, then sinks, outdoor shower, and continue until all water lines are done. I am sure to cycle some through the hot water heater. I also drain the heater after I'm done.
Then in the spring just hook it back up to water and flush it all out.