I keep this soap on hand all the time. It takes a few days to set up but it's really easy to make and works well in soft water. People with hard water will want to have it softened with borax or washing soda before adding soap.
1 gallon heavy plastic or glass container with wide mouth
1/2 gallon cold water
2.25 ounces lye
1 lb lard, melted
1/2 cup washing soda
1/2 cup borax (up this to 1 cup if you can't find the washing soda)
Fragrance oil or essential oil of your choice (optional)
Hot water to fill the container
Add cold water to container. Add lye; stir well (this barely gets warm because lye is so diluted) Add lard, washing soda, borax, fragrance oil. Add hot water to finish filling the container and stir well with a wire whisk.
Whisk 3 times a day or so until set up. Initially, it will start with a glob of soap on top but will set up more each time you whisk it. After three days or so, you will be left with a nice, powdery liquid that you can use in your laundry.
Add 1/2 - 1 cup for a top loading machine. Dissolve in hot water before adding to a very cold wash. Otherwise, just add it while the machine is filling. Use less in a front loader; this one WILL suds if you add too much.