Fresh water tank vents/overflow

[BouseBill]

On our 2015 Bighorn fresh water tank, there are two vents/overflow outlets, one on the drivers side and one on the door side. When ever the tank is full the water will start dripping out the drivers side.
I have a RO system plumbed into the fresh water tank due to the quality (very poor) of water at our winter host gig, so it's a very slow and easy fill of the tank. The vent/overflow on the drivers side was installed BELOW the level of the water sensor so the water tank never shows full, (confirmed by the service department). Now for my question.
Is it normal to have TWO vents/overflow locations on the water tank? What would be the ramifications of installing an on/off valve on the low side so the tank will completely fill with RO water, and flow out the high side when completely full?

 

[Geodude]

It's normal to have overflows on each side.

I have shutoff valves on mine. One side will always start to dribble first so that one gets closed then I wait for the other one to dribble then close it off and then shut off the water supply. I have the shutoff valves are attached to the levelling jacks. I don't have any good pictures of them but you can sort of see it here. The red handled is the valve. It's in the closed position because we just filled the tank:

 

[Lynn1130]

I have three one front off door side, one rear door side and one rear off door side. I have shutoff valves on them and when I fill I shut them off as they begin to trickle. This is important when we dry camp since I could lose up to 25-30 gals while traveling due to bumps and turns.

 

[BouseBill]

Thanks for the replies, I kinda thought it would be OK, but wanted to check with others here first.

 

[dbbls59]

Just don't forget to open one when you start pumping water.

 

[BouseBill]

One will always be open

 

[Redrider007]

Thanks for the reminder-My RV never shows full and God only knows how much I am losing on the road-Will look into shut off valves this week!!

 

[SNOKING]

I just push two of these on the vents. Chris

http://shop.tooltimehardware.com/images/Caulking Cap Retail Package.jpg

 

[Redrider007]

Do you just leave these on all the time? I figure the water will come out the breather when completely full or blow that cap off under pressure-Looks like a good option in case you forgot to open a valve.