I don’t use soap, but I use a stainless steel scrubber and hot water and thoroughly scrub the whole thing inside and out. I then dry it over medium heat on the stove, put a thin layer of oil all over the pan with a paper towel and then “bake” the cast iron in the oven at 450 degrees until it starts to smoke and stink. It kind of smells chemically.

https://www.amazon.com/Lodge-L14SK3-Skillet-Cast-Black/dp/B00063RWUM