I don't always have to clean the grill all the way but I do clean the slot below it. That would be the casting that the grill sits on. I use my dowel for this because it doesn't pull out any reds as easily as the notched end of the knife. With the dowel, I push the ash back until the flats of the grates are mostly bare. That way the air gets up across the glass and behind the grill.
When everyone knifes the grates, do y'all remove the plate casting that covers the area under the grates and above the ash pan? I do but only when the fire bridges and I can't get a good look at the center valley in the grates to see what's living there. Then I'll knife and/or dowel 'em till they move one
That might be once or so a week, maybe longer.