I'm not sure what type of vent, just a vent for the air, so the drum doesn't collapse in on itself. I can't remove one of the bungs because the drum will be on its side. So water would pour through the other bung if I did that.
Didn't intend to have a Deere fleet - it just happened 310C, F915,102, 5200 & 5065E
It's a simple solution. Screw a 3/4 street elbow into the upper hole. Extend with a short length of pipe ( 3 inches)over the drum. If the 2" hole is on top, you'll have to use a reducing bushing/s
we use drums of concentrated coolant at work and just put a ball valve into the 3/4 hole, tip up on the stand and just crack the 2 in bung a little so it will suck air when the internal vacuum rises. once the level gets down it's easy to crack it some more. the valve allows easy filling of small pails to dump into the machines.