This yields one and a half gallons of detergent.
Baking soda or Washing Soda - 1/2 cup
Bar Soap - 1/2 bar, shaved
Borax - 1/2 c. [optional]
Water - 1 and 1/4 gallon
Bucket or plastic laundry detergent container
If you use Baking Soda, you have to bake it at 400 degrees F for about two hours for it to become washing soda.
Boil one half gallon of water and dissolve the soap shavings into it. Meanwhile, fill your container with the rest of the water-hot tap water. Dissolve the washing soda into it.
Combine the two mixtures, cover, and let sit for 24 hours.