I use fine grit sand paper or a wire wheel. Or a 50/50 mix of vinegar and water, but only for a short time, like an hour or two.
Taking off the carbon and sludge I use a 5 gallon bucket of water with 12 oz of lye.
UDS - Midi Me - Weber Performer - 22.5 Weber OTG - Weber Genesis - GOSM
White Lightning Thermopen