[header] How to prepare used cooking oil for biodiesel [title] Obtain used cooking oil. [step] Locate a source for vegetable oil that has been used in cooking. Contact local fast food restaurants, cafeterias, hotels and other commercial food establishments to see if you can take their waste oil, or pay a very small fee for it. 
You may compete with rendering companies, who also pay restaurants to take used oil off their hands. [substeps] Try a restaurant that sells a lot of fried food, like french fries or fried chicken, as they are very likely to have large quantities of used oil that they need to dispose of.