Track run a 12mm vent pipe from the highest part of the tank.
They fit this with irrigation fittings, hose barb into the pipe, with a thread left exposed on the other half of the end fitting.
They then screw a spray jet onto the threaded fitting, completing the breather.
It's tucked up on the side of the bodywork out of sight. Just looks like a knob on the hose end.
On the Ute it could be situated on the headboard behind the cab body and pipe run down to the tank.
If your breather is a hole in the top side of the tank, you might have purchased the wrong tank.
There should be a proper fitting to fit the vent hose to.
Some filler necks will also have a extra pipe fitting that runs into the neck near the cap.
It's for fitting the vent hose to as well, Like a petrol tank. Only works when the cap is off.
Except it doesn't work well if the cap seals the tank, preventing air filling the void when you use the water.