Originally Posted by Iwannacamp
Ok. You got me... Please explain the siphoning and overflow deal. I am sure I am not the only newbie wondering about this.
On some Georgetown motorhomes there has been a problem with the water in the fresh tank sloshing around, especially in hills and mountains. This causes the overflow hose to start siphoning the water out of the tank. Users report arriving at a campsite with a less than full tank. Other RVs may have a similar problem, it depends on the configuration of the tank and overflow hose.
The key is to prevent siphoning if the problem occurs. Two ways to do this are to install a valve, or a vacuum breaker. Both are easy to do if needed, with inexpensive parts available at a hardware store. Some have rigged an automatic valve, but I just installed an simple ball valve on the overflow tube near the tank that I open and close as needed. The valve is closed if I am driving in mountains with a full tank of water. Open the valve when filling and using the water tank (very important).
A vacuum breaker is an opening to the atmosphere to equalize pressure in the overflow tube and prevent siphoning. Some install a T connector and some additional vertical tubing, or you can just drill a small hole in the top of the overflow tube at the highest point. These things are only needed if you are experiencing a siphoning issue with your fresh water tank.