This laundry detergent is so easy to make — but includes a little grating. Measure and add the super washing soda, grated Fels-Naptha soap, and grated Castile soap to a small saucepan. Super washing soda, Fels-Naptha, and bars of Castile soap can be found in the laundry aisle of most grocery stores for only a few dollars each. Super washing soda is a an all-natural product that kicks up your laundry detergent, and Fels-Naptha naturally cleans clothes along with the Castile soap. Cover with four cups of water, and bring to a simmer until the soaps melt together.