Wow, almost 2 years later now.. just an update about this A/C problem of mine since I originally posted.

Giving that tube a squeeze once every 6-8 months or so worked for awhile, but this spring it wasn't helping anymore. Maybe it got backed up in the hose further up than previously.. not sure. I had a mechanic try blow it out as a quick fix, but that only worked for a day or two. So then I had him take the hose out and snake/clean it. (Also got an A/C recharge too..)

Since then the problem hasn't occurred.. and I also stopped getting mist through my vents.