I use a very very gentle cleaner for the whole bike and it cleans off the soot from the muffler while using the wash mit used to clean the bike.
No abrasive or caustic anything is used on my LT.
Its Suzuki Bike Wash. It comes in a spray bottle or in a 1 gallon refill. Use it straight, no dillution necessary. This stuff is amazing, leaves no residue and takes the bugs, brake dust, and exhaust soot, no scrubbing, just wash as normal once sprayed on. Works well on tar too.
I use this stuff on everything, it does not harm plastics, windscreens, brightwork, doesn't dull aluminum. I also use Eagle One car wash soap for the remainder of my vehicles. The Suzuki Bike Wash gently takes off the difficult stuff.
My Honda dealer turned me on to this stuff when I was fighting the brake schmutz on the Wing's wheels. They are just about sold out every time I go to get more.
2005 330 CI Convertible