I used the term "spill proof" to mean the cap wasn't ventilated, and that might be the wrong term. Just meant if they fall over in the trunk and the vent doesn't get popped open nothing will spill. My 5-gal can has no vent to pop, but the nozzle is vented. Goes blurp, blurp, but never stops flowing. My smaller cans have vents that pop open. The 2-gal (maybe it's 2 1/2) is easiest to use. It has an upper cap you screw off, and a flexible nozzle with stops on both ends. Just pull the nozzle up, pop the vent and pour. The 5-gal and 1-gal have stiff nozzles in the jug that have to be reversed, and a cap plug that has to be set aside when using them. Messy compared to the pull up nozzle. I nearly always spill a little gas. Just have to top off. Can't resist. I didn't pay any attention when I bought them 8 years ago. This might be a real "no spill."
--Vic