My wife and I picked up our new ST20CK in October and had it winterized when we picked it up. The dealer spent about 2 hours trying to figure out why they were encountering the same problem you are. Turns out there are two valves to turn to bypass the hot water heater and someone at the factory had installed one (or both) wrong. Once they got that figured out it sucked antifreeze like a champ. My owner's manual doesn't say anything about the plumbing, so I plan to trace the plumbing next spring so I have an idea how the heck everything works. And I plan to go camping with it too for the first time!
If yours is new, I'dmention that tothe dealer.
Watertown, WI Edited by: KA9DQK