To a foaming soap dispenser, add the water first (to prevent bubbles) then the liquid castile soap followed by the oil. Shake the ingredients together.
Shake the soap dispenser before using, then squirt a small amount on your hands as needed, rinsing with water.
If you use distilled water, the soap will last at least a month. If you use tap water, use quickly within a week or two.
Notes
The idea is equal parts water and castile soap. Adjust the amounts according to the size soap dispenser you're using, reducing the oil as needed.
What type of soap dispenser should you use?
A foaming soap dispenser must be used. You can refill an old foaming hand soap dispenser, like a Mrs. Meyers bottle, or buy a new bottle off Amazon or a home store. Either option works, just be sure it's a foaming soap dispenser. My favorite foaming hand soap dispensers: