My new MFLB - help!

Hi Trees! I just got my new mflb from the entgiving sale, and I vaped my first bowl out of it last night. When I emptied it out, I noticed that the "trough" was a bit ashy, as I must have scorched the trees a tad, though I didn't notice this happening when I was using it. I can't seem to clean this out using the included brush. Is this supposed to happen? Any way I can clean it completely? Or is this just the nature of the mflb to get permanently "dirty"? PIC: http://imgur.com/TMVz8