When a Grill Brush Fails, Use a Steam Cleaner
This is the heavy artillery. It takes a long time, so this is not something to use after every cook. I use mine once a year to deep clean my grill grates and to de-gunk the deflector plates on my pellet smokers. These steel plates lie directly below the cooking grates and can get mighty greasy. Steam does the trick. This steamer comes with plenty of attachments, including 2 extension wands, scrubbing heads, and a brass bristle brush, all for less than a hundred bucks. Also comes in handy in the kitchen and bathroom!