Late 379 A/C drain issues

Have an 05 379,04 build date, that keeps pass side carpet wet. Condensation will drip some out of drain tube towards middle of firewall when running, however, when you shut A/C or ignition switch off it will immediately dump about a pint or more right out of drain tube like a soda fountain. Only filter I know of is the one under glovebox with knurled thumbs crew holding cover on and it is clean.

 

Can someone please tell me a somewhat non destructive approach to getting inside the box to clean evaporator and enclosure? Like I mentioned earlier I have done this on an early 379, like a '93 and it was rather involved but not like i had to take dash out. I have changed out blend door motors on this '05 but that is it. Really it works good other than soaking carpet but when you look in filter alot you can see a cruddy build up on find. I never liked that from a respiratory standpoint long before Covid 19