Loosing water from tanks when going around corners

Saw it on the road again today, a trail of water on the road around a corner. had a discussion about a week ago with a vanner who had a similar problem. His van had not been fitted with a breather hose and he had drilled a hole, top rear on the side of the tank, but going around left hand corners he lost water. Some trips in Tassie with uphill and downhill corners up to 1/4 of a tank

I suggested that he widen the hole and screw in and silicon a fitting with a about 150mm of hose attached. On the end of the hose is a tap that he can open when he is filling the tank and close when he is travelling preventing the water spilling out.

The problem with this simple fix, is that every time you stop for a cuppa, to stop the electric pump labouring, you have to open the tap for air intake into the tank. I suggested that he then fit a T section in the hose between the tap and the tank and then fit a 12volt valve similar to those used in watering systems. The valve being opened either by a relay of directly from the conatcts that start the electric pump, in this way. every time the pump operated the valve would operate and allow air into the tank.

He would still need to operate the tap manually when filling his water tank, and of course use the correct type of hose so his water does not develop a plastic taste.

Having said all of the above, the valve concept is just a theory has anyone done this sort of thing for real.

Peter