1. Since I can see AC water dripping below the car, at worst, I thought perhaps AC drain was partially blocked and was draining slowly.
But when I pulled out the AC drain host that was just adjacent to the cabin filter housing, no water had accumulated in the AC drain tank and no water came out.
I didn't have compressor handy, so I did use the shop vac (while sealing it tightly) on the AC drain hose and try to suck out anything stuck there.
It appears nothing came up, so I think the drain is good.
2. I trace the drain line, and it appears to go through the firewall, but I can't seem to find the outlet.
Perhaps, I have to remove the cowling as suggested above.
3. After changing the cabin filter, when I turn on the AC, the first 10-20 seconds smells pretty musty, then it seems to clear up after that.
I'll see if I can improvise something to clean the cabin filter housing.
Also, I saw some YouTube videos where they spray Lysol from outside intake while running the AC full blast with windows open.
I'll give that a shot.