I have a propane smoker, the tall rectangular box style with 3 racks. It is propane driven, I use Pecan wood logs from Academy Sports. A friend borrowed it cleaned just the outside. (Or so he claims.) I have been getting a dark black residue on whatever I cook since then. I washed the interior completely and it is still occuring. I have not changed the gas tank yet, will try it. It is a greasy residue in that if you touch it with your finger, it will transfer to whatever else you touch. When I slice my meat that I smoked, it gets all over the cutting board as well. Does anyone have an idea of what that might be and how to eliminate it? We had some babyback ribs it coated them and ruined the enjoyment of eating them because we were a mess!! Thanks in advance! BTW, Frisco as in Texas. Not the home of Nancy Pelosi.