Help!  I am new to living in a rig, a 1999 National Dolphin, and I am loving it! However, I am having issues on filling my water tank.  I have filled it 4 or 5 times now, and two of those times the water drained out of the air escape hoses and drained all the water I just put into it. I called Camping World, but their service dept was not in, and the parts guy told me it might be the rigs drain. He said it was the outside shower. I looked in that compartment and there is nothing that indicates a drain, other than the black and gray water drains. I read in the manual that when the water is filling, the air will escape from the hoses under the rig, and then when full, excess water will come out. The 1st time all the water drained out, I refilled shortly after, and had no problem. However, moving 150' of hose is not convenient, not to mention the waste of water. It is very frustrating. What am I doing wrong? How can I stop all the water from draining out?