I spray the inside with cheapo canola oil, using one of those 20 oz squeeze trigger sprayers, firebox too,
I recommend keeping a full bottle handy , and spray the inside before and after each use. It will make the smoker much easier to maintain. The only time I rinse mine out is right before I get ready to cook, usually just drain off any liquids and pick off the left over it'd bits, and sweep out the firebox with a brush. The times I did wash it after cooking, I ended up with mold growing inside. Never happens when I just leave it dirty, something about the heat and smoke I guess?....