In a glass bowl, add baking soda, citric acid. Combine and add essential oil.
Spray a couple of pumps of water at a time and then combine after each addition. You don't want to add water too quickly because it will react with the ingredients. Keep adding water until the mixture will hold together in your hands.
Transfer to silicone mold or ice cube tray and press into the molds. Allow to dry overnight. Then pop them out and store in an airtight container.
Just drop one in the toilet, allow to foam and then if it a quick brush and you're done!