Murph,
I'm not trying to answer for anyone and just want to throw this out there. I have read up a little on this:
I believe the term is called "Bucket Chemistry".
Collected waste vegetable oil has to be strained and cleaned down to less than 25 microns, the same as diesel fuel. The process usually takes heating the collected oil and a series of filters to accomplish. Mixing ratios of Diesel and Veg. oil provide these results (U.K Tests) - 10%/90% worked in all engines tested; 25%/75% dramatically changed the exhaust smell and 33% worked all year long. A 50%/50% mix congealed during winter months and needed additional thinning....but worked well during the warmer months.
There are several re-fit kits that convert your diesel engines to run on 100% filtered vegetable oil, but are expensive (according to the UK tests).
Mark