I've been told that you cant use any drums that have had motor oil, toxic sludge, chemicals, and the like. You need something that had corn, flour, ediable things in it only. I can find a whole bunch that have hand numerous no no's in them but none that have had food in them. Im not sure why you cant use just any ol drum but I guess it kinda makes sense.
Can you find one that has been used for industrial alcohol? Straight denatured alcohol can be cleaned out (beware of fumes), is non petroleum and harmless after a grill seasoning.