Funny thing but I used to work for a company who reclaimed cooking oil for the animal feed industry. At the time we used to buy stock from kitchens, but now I believe they charge for collecting it. Proctor & Gamble sell filter kits designed for cooking oil, and I wouldn't mind betting, your local caterer would have no objections with you having his waste. Be careful though, old oil forms longer polymer chains and as a result gets thicker. Also, don't bother asking at your local chippy, most of their oil is lost in absorbtion and they tend to top-up more than change.