The hose attaches to the low point or bottom of the plenum where the A/C evaporator is located. I've had them clog up, what I've done is disconnect the hose at the plenum then use a wire to 'roto-root' the hose and the opening into plenum. The other thing you could do is figure out access to the plenum and use a little bleach in there to kill the mold and algae that does the blocking. It also helps release and flush out the dirt and leaf crumbs that get in there.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI