Grate your Fels Naptha Soap using a cheese grater.
Add 4 cups of hot water to a medium to large pot.
Add grated Fels Naptha soap to water in a pot and set on the stove at medium-high heat. Stir until the soap is melted completely.
Fill your five-gallon bucket 1/4 with hot water or a 2.5-gallon bucket halfway (about 20 cups of water).
Pour in the soap mixture and stir until it is well incorporated.
Add Washing soda (or borax) AND baking soda; continue to stir until they have dissolved.