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The lid on those is pretty easy to remove. I would remove it and set it on ground and give it a good rinse with the hose or pressure washer. Let it air dry in sun and re attach
Bring the grill up to around 700°'s for about 20 minutes and it will burn everything out of the inside and the top vent. After it cools just wipe off the gray ash from the inside and you're ready to go with your next cook.