I've been trying to tackle this issue for awhile. I've been looking and studying at images on eBay/google/etc of the blower motor assembly. The tube under the filter stood out and noticed that it goes to where the AC drain is. So today, I bought a can of AC foam cleaner, stick the tube as far as I can go. Gave it a few minutes and checked underneath the car and its slowly draining down the AC drain tube!
DO THIS AT YOUR OWN RISK!
The blue box I believe is where the AC drain is and the yellow box is the tube to the cabin filter cover.