I've heard mixed reports about the vegatable waste residue that straight veg oil leaves behind, but then I've had loads of trouble with a waxy resiue in the biodeisel I was using. In the end I was spending what I saved per tank on new fuel filters so I stopped using it
Be very careful sticking waste veg oil into your truck. When heated, veg oil forms free fatty acids. I don't recall the reason these are bad, but they are.
However the 200TDi will run on vegitable based substitute fuels, whatever you choose to try :)