Fresh water loss while driving

JaxDad wrote:
I'd be surprised that you get much out the overflow / vent pipe. They usually mount them a little ways above the tank to prevent just that from happening.

If though you are getting spillage, I would definitely suggest a simple floating ball check valve over a standard ball valve. First because it's automated so there's nothing to forget to do. More importantly though because to eliminates the possibility of damage to the plumbing in the RV.

A floating ball check valve is a little device that looks a lot like an inline fuel filter. Inside the body of it is a little hollow plastic ball that gravity drops down into a recess to mostly close off the opening, enough air can pass to allow for normal operation though. When however water comes up the line the ball floats, rises into an upper recess and again mostly blocks the opening. Enough water can come out to tell you the tank is full, not enough to cause an issue.

I wonder though if the real issue isn't that your RV, like mine, has twin water tanks. In my case one under each dinette bench. There's a crossover line about 3/8" between the two to balance them out. However that little line underno pressure save the water weight itself is extremely slow to equalize the tanks. If I fill the water with a hose and stop when water appears I have one tank full and one tank 1/4 full. If I leave it sit for a while and recheck, I have a reading of 1/2 a tank of water because it's now divided between the two.

I can't speak for everyone but my tank will overflow and create a siphon want the water starts to flow. Ball valves are a simple solution that solves the problem. Yes you need to remember to open them upon arrival