WHen waste tries to go into the tank of the Sani-flow, it must displace air (out). An AAV only lets air in, so the waste will have a hard time getting in. That's why it needs an atmospheric vent line. Yes, run it into the attic and then attach it to an existing vent before it goes through the roof, or make a new penetration specifically for it. You'd be better off connecting the vent from the sink to this same line rather than using an AAV there.