Grind 200g of Fels-Naptha soap with an old coffee grinder. Anything works really as long as you can get it down to powder.
Add 400g of Washin Soda, and 400g of Borax to a plastic container
Seal the container and shake to mix
Use about 2 tablespoons per load
Notes
I’ve tried using Zote soap, another popular laundry soap, but its way to hard to grind into a powder. The soap is not nearly as dry as fels naptha, the texture is slightly oily.