Quick,
After letting the foam work, when I patch it out naturally the patches push some gunk out, and capture more on the patch. I can patch till I run out of patches without getting a clean patch, unless I help things along a little with Butch's or Hoppe's , or cr-10, or something to get that last bit of black out. After I do, I foam it again and the clean patches stay that way, the foam doesn't change color and everything comes out easier too. I know dang well it's clean then!
Jim