Fresh water tank fill issue

I also have a Vibe and had the same problem you had. Additionally, starting out with a full tank & after traveling 1hr the tank was only 1/2 full as it empties via the overflow which is underneath beside the drain. My solution was to remove the outside shower which we never use and move the overflow to that area so that the overflow outlet is above tank level. The design problem is that the water tank is totally under the floor where the slide out travels over it and there is no way near the tank to get the overflow above the tank. For a time before my mod I would fill the tank until overflow, then close a valve I added to the overflow for travel, and then open the overflow valve when setting camp so that water tank walls would not get sucked in by pumping water from the tank.