Outside surfaces – Use a warm soapy water solution to clean, then rinse with water.
Inside surfaces – Remove the top unit of the Otto Grill by opening the two fasteners located at the back of the grill, sliding the entire top unit into this direction and lifting it from the bottom unit. Place the top unit with its outside surface onto a towel, such that the two ceramic burners are visible. Now use a warm soapy water solution to clean all stainless steel surfaces, then rinse with water to remove all soap residues. For stubborn particles, a non-metallic brush can be used. Handle the top unit with extreme care and avoid exposing it to shocks, as this can easily cause damages to the ceramic burners.
Cast iron grill grate – Clean with a suitable stainless steel bristle brush. As needed, remove from grill and wash with warm soapy water, then rinse with water. After cleaning your cast iron griddle, dry it with a towel and wrap it into a cotton towel for storage. From time to time, treat your griddle to a grease rub using vegetable oil (e.g., flaxseed oil).
Via the following links you can find a video which shows how to clean the O.F.B.