I read an article in Landline Magazine last year. It was about an OTR trucker that made his diesel from the oil of the fast food joints in his town. He had added 2 extra filters on his truck, and had several "settling" tanks in his shop. He said that his biggest problem was the time required for proper settling of food debris in the oil. Apparently even a week was not enough time for his specs. However, he added the extra filters on the truck to accomdate this.
Also, being a big truck driver means that he needs a lot more fuel than most of us would. But the thing I got from the article was that it is a time intensive project. After the initial setup cost, how much driving do you do, how much time could, and would, you want to keep after it. How long would it take you to recover your costs. And finally, could you use it as a tax deduction for your business?