A tool you might want is stick blender. It helps mix and turn the soap liquidy. I found one at the resale shop for like $3 and it's strictly for soap.
You will need a gallon of water, 8 to 10 ounces of your favorite bar soap and some avocado oil. The oil is not necessary but it's really great for your skin. I use about a tablespoon.
Grate your soap or cut it really finely. Bring the gallon of water to a boil. Remove from the heat and add the soap. Stir to help the soap disolve. Then just let it sit for 8 to 24 hours. It will turn into a glop of soap. Blend it, stir it, mix it up. You need to turn the glop into a liquid. Now just store it in your gallon container and in your body wash bottle. It's ready for use.
I love this stuff and I hope you will too.