I had this problem. What I did was bought some flexible ducting and hard ducting and ran the duct from the grow box to the closet. In the closet I cut a 3 inch hole in the roof, in a out of site spot, and ran the duct into the attic of the apt. The i climbed in the attic and found the bathroom vent. The bathroom vent runs from the b-room to a vent on the roof. The bathroom has a vent fan with a 3 inch duct to the roof vent. I then attached my 3 inch grow box duct to the roof vent, using some of the b-room duct. I put a booster fan in, towards the end of the run to help with flow. So any smell ends up on the roof, blown away.

I saved the drywall hole I cut out of the roof in the closet. When I moved out I put the piece back in, and you could not even tell there had been a hole, and then i reconnected the bathroom vent.

good luck