I have an CB750 K2 oil tank that has fresh powder paint.
Inside thin layer of rust I'll remove with vinegar for some days. After that flush with water, blow clean dry with air and all dust out. End with white spirit (std degreaser), shake it good again followed by a thin layer of oil and shake it to protect all surfaces inside.
No small parts in tank that will enter the oil pump direct without any filter nor strainer.