Usually, used cooking grease or oil is filthy and requires some amount of cleanup before it can be converted to biodiesel. Unless the bio plant is equipped to do this, it usually goes through a secondary outfit that does this. (here’s one example - Cooking Oil Recycling, Disposal, & Hood Cleaning Richmond)
Also, there is a mechanism in the EPA’s RIN generation system that requires the generator (the biodiesel manufacturer) to disclose and list the supplier of the feedstock to assure they are on an approved list. This EPA-maintained list determines what type of RIN can be generated and what class of biodiesel can be made from it. (RIN stands for Renewable Index Number) These RINs are then sold to companies that do not want to purchase and blend renewable fuels into their products (Exxon, Shell, Chevron, etc.) That’s why the EPA administrator giving “hardship” exemptions to these companies have crippled biodiesel companies. The RINs were a way of leveling the playing field. Tipping it to the big boys has effectively wiped out the small biodiesel producer (like me).
ETA: - I do not know what record keeping grease collectors must do to make sure their collection of used grease is not stolen.
