exhaust out your sewer vent pipe?
 

Quebecgold,

Have you considered running your exhaust out your sewer vent pipe? Usually, there is a Y where the tree comes out of the concrete floor in the basement. Both the pipe and the dryer venting are about 4" and can be easily mated up with duct tape. This way, the air/smell will exit through the top of your building, where prying eyes are usually not looking. I've been exhausting like this for over 2 years at a couple of different places and have had no problems so far. My exhaust is running full time. If your exhaust is off and on all day, consider using a smaller exhaust fan that you could leave running all the time.

Hope this helps, happy growing, Schmikey

Excellent idea. You can also use chimneys if you have an access.