This was my reply in a similar thread.....
Heck....I just open the door and rub the inside of the glass once a week with wadded up newspaper and then just chuck the wad on the coals when I'm done.
But with a related question.......I only find my glass getting dirty when I shake the crap out of the coal after a good 8-10hr burn. And even then, the glass is always easy to clean ( I do it about once-twice a week).
So how does some members' glass get dirty to the point that it's hard to remove? Where to those 'tough' deposites come from? Impurities in the coal?