You should be able to buy a kit so you can use the existing water pump to winterize the system. I did it on my 2002 Sunline. But if that didn't work, you could use a pond pump or bilge pump to pump the rv antifreeze into your fresh water tank. Just put the pump at the bottom of a container, fill with antifreeze and have a vinyl tube from the pump to the water inlet. I use a pond pump to pump water into my fresh water tank when I camp where there aren't any water hook-ups. Link for kit:
http://www.amazon.com/Camco-36543-Pump-Converter-Winterizing/dp/B0006JJ588