Nice to meet you Budz, thank you for your comment. My dad was a plumber and the Idea came to me while helping him on a sewer replacement from the house to the street. I noticed a steady suction on the street side of the sewer from the water flow on the main street line, this suction carries...
The fan discharges in front of a backwater valve so the air can not blow back up my stack. no heat signature. The fan blows at such a high rate that the air is forced in to the sewer system where the suction from the water flow pulls the air down line.
Pot odor is diluted with the sewer smell, Been doing this for 12 years with no problem. As far as cops with their infrared cameras, pumping exhaust into the sewer will show no heat signature like the exhaust from a carbon filter discharging through a house wall. I agree, carbon filters do work...
I have a grow room in my basement with and use a heavy duty exhaust fan with a 4" discharge. I removed the sewer cleanout cover in my basement, extended a 4" plastic pipe from the cleanout to two feet above the floor and attached the fan discharge to the pipe. All the smell from my grow room...