Why do you want to do this, George?
Are you trying to get rid of odor inside the boat, or only out the vent when you flush? If you think that re-venting the tank will solve odor problems inside the boat, it won't. But even if you only need to do something about odor out the vent, installing a second vent line and a fan isn't that simple. Besides, we've had enough discussion about the effects of urine on aluminum that you should know your aluminum tank is almost certainly living on borrowed time. If I were you, before I went to the effort and expensive to revent it, I'd replace it with good quality plastic and work out the proper ventilation in the new installation.But if you determined, I'll help you figure out how best to do it on your boat if you want to give me a call next week. 800-352-5630