if your running a vacumn on the cabinet you shouldn't need the other hole.
I don't see your cabinet so I'm only guessing and all I have to compare it my skat blast cabinet. I have the vacumn hooked to mine and there is no other holes...even from the factory. In fact, there is a seal around the doors to make it "air tight" so to speak. This is so the vacumn can suck out the dust. As the media breaks down it willg get dusty and worst as time goes by. You can't see, and most likely the media isn't cutting very well either.
Seal up the holes, put in some new media and let us know what happens.
