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 :)