Would a tank that used to hold diesel fuel but hasn't had any in it for years work as a smoker if we really clean it out and sand blast the inside?
Used heating oil tanks (heating oil is essentially #2 diesel fuel) are commonly used for "clamshell" smokers and grills in the Baltimore area. Many of these guys are preparing food for sale to the public, so I assume the health department knows of and has approved of their doings.
I've also seen a great many in use in NC.
I would clean it as best I could and then build a very large fire to burn any residue away. I may even do this a second and third time.
P.S. If you die, please let us know.