Here in Iowa we have soy-biodiesel, made from soybeans of course. There are different blends of it, 2% up to 20% that are available. Highest I've run is 5%. I don't know about having to drain everything, I just fill my tank and go. There is concern with running a 100% biodiesel, the rubber (gaskets, o-rings) in the engine may not be the right material and the biodiesel can eat away at it. In later model vehicles it shouldn't be a problem, but something to watch out for.