I’ve been using P21S polishing soap for a while now. The selling point of this stuff is that you can use it wherever you would use a metal polish. It’s a water-based soap that’s biodegradable and non-toxic; it requires minimal effort to prepare for application.

When I cleaned the exhaust tips on my GT4, I simply took the enclosed sponge, wetted it, shuffled it around in the soap, then lightly scrubbed the tips. Depending on your exhaust setup, you may have to use this more often during your car washing, especially if you don’t have cats (Catback exhaust), as I do on my e92 M3.  

I like how it isn’t greasy and doesn’t leave crap underneath my fingernails. A super-effective, super-efficient product that gets the job done with a fraction of effort. 

There are other uses for this, like cleaning stainless, aluminum, glass cooktops, etc. My primary use for it will be cleaning my exhausts.