Yup, all bets are off when you said some DUMB A** thought he knew how to run veggie.
After those easy things listed above, switches and coolant tank, I'd be really suspicious that veggie is plugged up in it, and whatever fuel pressure you were generating was bypassing or not getting through.
Others are smarter than me on this topic, but maybe open a fuel line to an easy to reach injector and then hook up the garden sprayer as noted in Pete's priming directions and see if you get some fuel?
(Great job on that write up Pete, I wouldn't change a word)
Will diesel act as a sufficient solvent on veggie sludge, or will more extensive cleaning be required?
happy coaching!
buswarrior