that was my original plan but I could not see a way to get a 3 inch air duct up to a deck fitting/vent that looked acceptable. what I have done instead is cut a hole in the wall between the battery/holding tank locker and the bathroom and put a fan there blowing air into the bathroom which will then vent outside through the existing hatch in the bathroom. downside is I will have to keep the bathroom hatch slightly open for the system to work but all in all a great way to vent bilge, batteries , holding tank ,sanitation hoses, and bathroom.Through a deck fitting. How else?