Go here...
Cleaned the Muffler
...for some info on cleaning up the muffler. I sort of combo'd the Nevr-Dull wadding polish and the fine steel wool, starting with the former and finishing with the latter. The Nevr-Dull starts the cleaning process and gets the surface moist with whatever kind of polish it contains; then I pick up the steel wool. It's been awhile, but I don't think I used steel wool on the tips---as I recall they cleaned up pretty easily without it. I think I finished by quickly buffing with an old microfiber towel (dry). I sort of thought I might be wasting my time doing the muffler, since I thought it would probably re-grunge pretty quickly. I was wrong: It's been since last fall (or even late summer) and it still looks very good. Took me and my kid about half an hour.
Actually, I should amend this a bit. I went out and looked at the exhaust (not having done so before posting!) and noted that, while the muffler still looks clean, it's no longer got the shine I saw after the above treatment. I'm sure 15 minutes with the Nevr-Dull (probably without the steel wool) would restore that.