I'm trying to get my 97 Mountain Aire ready for a trip. When I attach an external water source, I get water inside at the sinks and shower but nothing seems to be draining out and the dump valve is open. I am brand new to this and don't know much and I can't find much about anything on these online in the way of information, diagrams, specific how-tos or anything. My understanding is this RV was likely winterized somehow but I don't understand that process to be able to "undo" the winterization if you will. ANY help is greatly appreciated.