WALLEW, sounds like you need my chemistry background. Call anytime.
This procedure is called transesterification, similar to saponification. Sound familiar? Saponification is soap making. To make soap you take a transfatty acid or triglyceride (oil or kitchen grease) and blend it with a solution of sodium hydroxide (NaOH, caustic soda or lye) and water. This reaction causes the ester chains to separate from the glycerine. These ester chains are what becomes the soap. They're also called lipids. Their unique characteristic of being attracted to polar molecules such as water on one end and to non-polar molecules like oil on the other end is what makes them effective as soap.
In transesterification, lye and methanol are mixed to create sodium methoxide (Na+ CH3O-). When mixed in with the WVO this strong polar-bonded chemical breaks the transfatty acid into glycerine and also ester chains (biodiesel), along with some soap if you're not careful. The esters become methyl esters. They would be ethyl esters if reacted with booze (ethanol /ETOH) instead of methanol.
So how easy is it?
Filter the WVO.
Heat the WVO to remove water.
Perform a small titration on a small batch to see how much catalyst (DRY lye) you need for the entire solution. [EDIT - you'll need to do a ph test here]
Combine the lye and methanol to create sodium methoxide inside of the WVO tank in about a 20% mix of the total volume of WVO.
Slowly stir, this reaction probably takes an hour, the transesterification process separates the methyl esters from the glycerine. The CH3O of the methanol then caps off the ester chains and OH from the NaOH (lye) stabilizes the glycerine.
(NOTE) This appears to be an EXOTHERMIC reaction, and it will give off heat. this is good, because you can decant the glycerine (brown stuff) from the amber colored fuel. If it gets too cool, I bet it would solidify and you'd have to reheat it to decant it.
Hope that helps some...