Originally Posted by mtedelen
Is it safe to put a valve on the overflow vent tube? I would love to if it is. I normally fill my tank full until water comes out of the overflow tube, however by the time I get to camp it seems as though 1/4 of the tank has emptied during the drive from sloshing around. Would like to keep that water in the tank if I can, just curious as to whether or not a valve on the overflow would force the water try and come out somewhere else that could cause damage.
You MUST have the valve open when filling and when you set up at your campsite (so air can get in as you draw water out). It should only be shut when you are done filling and while you are travelling.
If you don't open the valves when filling, the force of water going in may cause your FW tank(s) to bulge or cause leaks at fittings due to added pressure.
If you don't open the valves when at the campsite, after a time, you may not be able to draw water because air cannot get into the tanks as water is drawn out.
This isn't a big deal, just make a habit of doing it and you'll be fine.
As to whether this would void your warranty? Possibly.