Get your self along the the forum I list in post 3.
None of this is as simple as it seems. Also if it's being done properly the places giving you the WVO need to track there waste disposal so you will need a waste licence form the environment agency.
IMO if they are going to give you free WVO then they are either mad as they can sell it or it's not going be much good for making fuel. My guess is it will contain a lot of animal fat such as found in kebab or burger joints. Animal fats will solidify at quite warm temperatures blocking fuel delivery systems.
Unless you have a Bosch diesel pump I think you are going to have a lot of problems. Really read and digest information in that forum.
Assuming you do get started what are you going to do with your waste generated from the refining process?