Works like a charm. It's a great solvent, as well as a lubricant.really WD40? I'll have to try that one...
Can't believe nobody's suggested it yet, but NEVERDULL!! It works awesome. It will clean up any tar, oxidation, and any other impurities. It will clean them up and give you a clean, new looking pipe. If you want to shine them like chrome, you will have to use other methods after the NEVERDULL, but it will clean them up relatively easy.