The first trick is to find the water tank. I would bet its under your bed--have you looked under the bed. Even if there is a panel there see if you can remove some screws to remove it (on the 24.1 the water tank is under the passenger side bed).
More than likely the valves for drain, winterizing, etc. are all in a compartment somewhere that you have to remove a panel to get access to.
Go here to find out from Thor how to get construction drawings (in this case the fresh water diagram will help you out):
http://www.thorforums.com/forums/f10...ings-5833.html