[v3d4]

for using used cooking oil, i have heard many people put in a second tank for the french fry oil that has an electric warmer because it wont burn if its too cold. so they start their engine on regular diesel and after getting going they switch to the other tank, and then before turning off the engine, switch back to the regular diesel so that none of the sticky stuff in the oil stays in your fuel pump/ engine.
otherwise used oil has to be treated to clean out the gross stuff that will gum up your engine
-this is all secondhand info that i have heard