Originally Posted by Motodad
I put a on-off valve on my vent line. I leave it open when filling and when it starts running out I turn off the water and close the valve. When I get where I'm going I open it and leave it open til I fill tank again. Works great for me and I usually come home with water left in stead of running out.
Motodad - You are in the very few category that seem to recognize the siphoning. As you probably know the vent is used for overflow and also to allow air in when you use the water.
As for your valve idea it is a way to stop siphoning, but if the valve is inside the water compartment with the yucky latches, that would be a pain. My pvc vent/ drain works good for me. Now we have two anti-siphoning methods. - Hank