Wire-spoke wheel brushes for cars work best, with natural fibers. The dirt/grime/grease simply doesn't stick to the brush like a nylon or plastic bristled brush. Just a pro-cycling pro-tip ;)
Coworker of mine had one, got it stuck in some sloppy stuff pretty quickly, then sold for a Subaru because it needed an air suspension compressor. He missed the 8 level heated seats, he said, and not much else.