I use baking soda, white vinegar ( 1 part baking soda to 2 parts white vinegar) in some boiling hot water in a bucket that is big enough for them to be covered with the water ( I dump this dirty water outside so that it does not clog the drain in the sink with the grease). Let it soak for about 30 minutes or until you have cleaned the rest of the kitchen.
This video give a few other ways of cleaning them. Check it out.
D&D Taking Out The Trash, LLC