Can someone please explain this. When we left for our trip i put just enough fresh water in the tank to use the toilet and wash hands while we were between campgrounds. At the first rv park i hooked up the fresh water and was checking the levels and it showed the fresh water tank was full. I thought the gauge was wrong then i checked the tank(no easy task) and it was full. That should not happen. Is there another hidden valve in this coach. Getting real tired of everything being hidden. They should have put all the controls in one place. Help!