If there is a facility in your community that collects hazardous waste they will probablly take it. There was a Household Hazardous Waste Site in my hometown (Tucson, AZ) that would take fixer but they only take materials from households and not businesses. I think businesses have to pay a fee to dispose of waste. If you can't find a facility try contacting a university or art school with a photo department and they might have suggestions. Or perhaps the manufacturer of the fixer can give you some leads.