I was lapping/refreshing/cleaning my Norton 1k after beveling a bunch of razors, and I found that even after lapping the surface, there was still some blackness left in the hone. I tried rubbing it with my fingers, cause that often helps, but no dice. I was going to grab a brush and start scrubbing, but I thought I'd try out the sprayer-thing first (this was my first time lapping in my kitchen sink). The sprayer did the trick. Hitting the Norton with that high pressure water took the blackness away. Now, I'm not sure if the black stuff was driven out of the hone and down the drain or deeper into the hone, but I'm guessing it came out.

So give it a try - shoot your Norton with a jet of water next time you're trying to clean it up; it just might work. And try shooting it before you lap - removing swarf first can only be good, right?