I have never washed cast iron grates before seasoning. just build a hot fire to burn off the manufacturing "grease/oils." then while they are still hot, like was just said, cook bacon on ALL of the grates, or melt some lard or shortening and wipe the grates with that. After a few more cooks, especially with something that has a fair amount of fat, you'll never have to oil or grease them again. Mine on my CB940X probably have enough grease in them to keep McD's happy for quite some time! LOL