How to clean soot out of muffler?

I want to clean the soot out of my muffler, but it would be to much to take it off, since its more then just a cat back or any of those regular ones u can buy. the previous owner of my car took the muffler off and welded a pipe on, so now its a straight pipe exhaust, it would be hell to take that off, is it okay just use soap and water? and just make sure the water duznt reach the cat??