Originally Posted by 5picker
Yes... there have been many reports of the fresh water tank emptying itself on movement of the R/V. Some folks have added a shut-off valve to the overflow line.
I would concur with all your other assessments.
On another note: Even with 53-57 gallons of fresh water, I'd be happy. We only have a 40 gallon tank. Time to trade?!!!!!
It's been suggested that the problem is not only due to water sloshing up through the vent during movement, but that you can have actual siphon action.
The siphon principle:
Remember that you can set a full glass of water near the edge of a table and insert a piece of flexible tubing into it, to the bottom. Drape the other end over the edge of the table and give it a quick suck to fill it with water. Water will flow until the glass is empty, even though that flow is uphill from the current water level to the rim of the glass. This is because the weight of water in the uphill portion of the tubing is less than the weight of the water in the downhill portion.
Now, put that tubing in the full glass, but only 1/3 of the way from the top and start the siphon. Water will flow, but once the water gets below the bottom of the tubing in the glass, no more can be drawn.
Now that I've gone through this tedious example, it will be obvious to you that the problem is that the overflow tube in your tank is sticking down too far into the tank
. In fact, it is sticking 1/3 of the way into the tank. You need to extract it until it is barely into the tank. Hopefully there's a way for you to get to it without dropping the tank.