I've used rubber valve stems to make vents with. All you have to do is remove the valve core from the stem, drill a half inch hole in the appropriate place for a vent on the jug, run a wire thru the hole you just drilled thru the jug and out the fill opening. Attach the rubber valve stem by running the wire thru it so the threaded end the cap screws onto comes thru the new hole first, pull it thru the jug and pop it in place just like you would on a wheel. When you need the vent, take the cap off. I have bought the replacement pour nozzles from Tractor Supply and they work well. I fixed my yellow 5 gallon diesel jug, plus my two 5 gallon red jugs for jet ski gas this way, and they work great. All 3 of those jugs came with the F'd up nozzles and no vents.