involving the ceiling vent? Thanks in advance. I rent so I can't do anything that I can't easily put back later. The cat litter is perfect in that closet but it has it's own HVAC vent (in a closet? go figure) so the stink flows INTO THE HOUSE. I got a venilation fan to lay over it and it sucks air OUT - perfect - but the A/C would be wasted out the open end of that duct, laying in the attic, after removing it from the vent. Perhaps I could do the next closet too, and just tie the two ends of these 5" ducts together with the proper ductwork piece (does it exist?). I'm thinking cable-tie hefty bag over the rim where the INPUT end of the duct goes after removing it at the A/C unit. It's typical aluminum foil tube with coil spring inside. I don't want to crush or damage it, as I must put it back some day when we move. THANKS!