You might notice a sticky dark gray residue on the inside of the caps. 

Clean the Water Misers using a baking soda and water solution to loosen the buildup inside the cap. Mix a 10 to 1 water to baking soda solution in a bucket or small bowl. 

Let the vent sit overnight to neutralize and break down any electrolyte in the caps. Next take a closed cap and force water through the vent holes in the top of the green portion of the flip-top. Water should drip freely through vent holes. This won't be a constant stream of water but, a trickle from all 4 vent holes. If water passes through the vent holes, you know the pathway is clear. Let the vents dry. 

Once dried, shake the vent to make sure the condensing beads on the inside of the vent slightly rattle. If you do not hear the beads, let dry for an additional 12 hours or repeat the process above.