Jews who keep kosher observe various religious laws, many of which pertain to food, both directly and indirectly. For example, kosher-keeping Jews don't use cooking utensils, including grills, used to cook non-kosher food. Grills used to cook non-kosher food need "kashered" to make them kosher. You must heat the grill until it glows, a process known as "libbun gamur." If you don't have experience using a blowtorch, enlist a helper who does.
Remove the grates and set them on top of a layer of charcoal briquettes. Put a second layer of charcoal on top of the grates, and light the charcoal. This should heat the grates until they glow, which constitutes libbun gamur. Alternatively, have a professional heat the grates using a blowtorch.
Blowtorch the part of the grill cavity that is level with and above the grates. This area of the grill may have directly touched non-kosher food, and needs libbun gamur.
Clean the grill cavity using steel wool and oven cleaner to remove all "mamshus," or the debris left from the cooked food.
Close the hood of the grill. Turn the grill to its highest setting and let it heat for 40 minutes. This kashers the inner cavity of the grill through a method called "libbun kal."