bdon and others wondering when the liner is burned out enough:
When it is burned out enough, you should be able to use a pressure washer or take the drum to the helpie-selfie car wash and simply wash out the residue. You can tell it is ready if it is whitish or pinkish and flat, and if you can run your fingernail over the cooled barrel inside and scrap off paint.
The very best thing I have found to burn out liners is a Harbor Freight weed burner, which saves a lot of time, and which you will later use time and again as a jet engine method of starting your coals quickly, so go out and spend the $20 or whatever and get one. Just start burning around the inside of the barrel with that thing, and it will remove all the inside and outside coatings.
Double-Barrel Smoker (DBS); Ugly Drum Smoker (UDS)