I've used either real coarse salt or water softener rock salt with isopropyl alcohol. Shake and soak, you can hear how clean it's getting by the noise of the salt on the pipe. Fill maybe half full plug the ends and shake by hand. If it's real bad do it when pipe is warm(not hot) and you may need to do second or 3rd wash. Works for me because I have any one of the mentioned products at home in big quantities.
Whatever works for ya. New parts are great too