I appreciate the replies but since on my previous RV that had a vent the same height from the tank and never had water flow out of it that I saw, it would seem there may be a fix for this.
Gandalf
That is perfectly normal. If you wanted to remove the plywood platform from the passenger side bed, you would see the inside of the passenger side hookup.
Essentially (at least on my 2551) the overflow tube attaches slightly higher on the tank than the fill tube. Thus, when you fill until the overflow bleeds water, the fill tube is mostly full (as is the water tank).
When you drive with the tank full, the water sloshes and pushes a small amount out the fill tube. This is especially true if you make a left turn, thus centrifugal force "pushes" the water up the fill tube and out the air vents.
The only way to stop that (that I am aware of) would be a flap valve on the fill tube and/or a fully sealing cap on the fill tube.
Take a 1/2 to 1 gallon of water out of the tank by running the sink for 30 or so seconds (after you fill the tank) and the sloshes should no longer be an issue.
Oh.. One more reason for the leakage, in the spring most faucet water is really cold so while sitting in the tank, warms and expands.. Raising the level in the tank. Again, perfectly normal and not something to worry about. But if it concerns you... Draw that 1/2 gallon or so and you should be fine.
Don