The recipe for making a basic survival soap is 2 parts grease to 1 part pot ash.
To make Grease: Take the fat from an animal and cut it in to small pieces. Cook in a pot or can over a fire with just enough water in it to keep it from sticking. Pour this grease in to another can / pot and let harden.
To make Potash: Take ashes from your wood fire. Put in a small can that you have a hole punctured in the side. Pour in water and mixture that comes out of the hole is Potash (Lye).
Mix these ingredients together (2 to 1) in a pot over a fire. Keep stirring until it thickens. Pour it in to a pan / pot let it cool. It will harden. Cut in to squares and then wash your dirty Prepping, behind!