Just had a very satisfying Sunday working on the stainless tips to my B3 3.3's exhaust.
Don't think they had been cleaned in quite a while so tackled them with gusto! (Wife thinks I'm mad)
Step 1. Pre soak with bio oven cleaner and then agitated with a wheel brush
Step 2. Second soak with common or garden alloy wheel cleaner
Step 3. Sponge wash with Fairy liquid
Step 4. Rinse and dry and admire all the filthy water that came off them
Step 5. Wrapped some flexi body sanding mat in a microfibre towel and
rubbed inside and then outside of exhaust tips
Step 6. When dust wiped away - repeated with a microfibre coated in
polish, first Brasso, then Autoglym
End result - can now see no carbon deposits on the outsides and the inner tips are silver for the first time in 12 years. The carbon / exhaust gasses had fused like black enamel and took 2 hours to shift. (A friend of mine can cut this down to 10 minutes as he has a Dremel with polishing pads for his M3 exhaust).
Will post some pics as soon as I get them off my phone