i think you can totally vent into the sewers, but you should be sure that your vented air cannot be tracked back to your house.

For instance, you would need to be far enough away from a 'service tunnel' so that your sewer line meets your neighbors before it can be accessed. If they could walk though the tunnel and look at individual house lines, they would probably smell your sewage & your buds. If it is the entire neighborhood, they could not check every house.