Put Fels Naptha in the fridge for overnight prior to making the recipe.
Add 1/2 cup baking soda and 1 bar of Fels Naptha to the food processor, process until the Fels Naptha is crumbly. Add to your bucket and repeat for all 3 bars of Fels Naptha (be sure to add another 1/2 cup baking soda each time).
Mix all remaining baking soda and other ingredients in a large bucket or plastic bag (be sure to use a face mask or avoid breathing in the powder particles).
Optional: Instead of scent booster you can use baking soda mixed with drops of essential oil (the oil will cause the baking soda to clump).
Add 2 tablespoons to the drum of your washing machine prior to adding in your clothes.