My mother is amazing at putting away (hiding) things. I was dammed sure I had all my containers already fixed, but suddenly two more appeared out of the blue when I was getting stuff ready for Dorian. Oh well, they have shed the Federal restrains and they will now flow freely as God and Fluid Physics intended.
You can get the vent gas caps at Amazon for an inexpensive amount. Make sure to drill in the flat area of the can for proper sealing.
Update: I ended up buying this three piece titanium step drill set and used the one with the 1/2″ all the way through. As I posted back in 2017, you will need the full 1/2″ hole rather than the 31/64″ (one size below 1/2″).
And a rubber mallet. Trust me, it is that tight.