If it starts getting too caked on, the carbon buildup can also start acting as a kind of insulator between the dish and what you put in it so stuff doesn't vape off as well anymore. I'm with
@archie gemmill , you can get it really hot to kind of bake the stuff up nice and crispy and then let it cool and flake it off, or iso soak. Haven't tried it, but I hear acetone can clean really well, also. Supposedly will leave more residue than isopropyl, though, so have to wash and rinse real well after and before using.