You have the dreaded red liner. People have reported that the red liner is harder to get off than the other liners. Like Chriscw81 said, burn/grind it or get it sandblasted.
As far as food safety goes, you can pick up a barrel that has held most anything and then just get a really hot fire to burn out any residue that may of been in it and then wipe down with rubbing alcohol to remove any soot or ash that remain.
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