1/3 bar Fels-Naptha
First you will need to grate the Fels-Naptha. I use my food processor to due this quickly. Next put the grated soap in a sauce pan and add 6 cups of water. Heat this until the soap melts.
Add 1/2 cup of borax powder and 1/2 cup of washing soda to the melted soap & water mixture. Stir until it is dissolved. Remove from heat.
Pour 4 cups of hot water into the bucket. Now add your soap mixture and stir. Next add 1 gallon plus 6 cups of water and stir. If you would like to add a fragrance to your soap you can add essential oil here.
Cover the mixture and let it sit for about 24 hours. During this time it will gel. I like to use my hand blender to make the soap a more uniform consistency, otherwise it seems to have clumps of gel floating in liquid.
Use 1/2 cup per load. I have a front loading washer and only need about 1/3 of a cup.