Use a dremel start with the sanding disks they work well but best in the open also double them up for strength they come in different grits you can start with a course grit then end with a fine then the polishing wheel its grey kinda soft. End with mother's mag polish with the dremel fiber/cloth wheel repeat as necessary.
Never tried to polish inside the tube might be a real challenge depending on how big the tube diameter is. If its not rusted or pitted just use the mothers mag polish and a drill adapter cut down to the right size diameter/length.