Update: 22 February 2011. I'm hosting a laundry soap making party next week and a friend of mine sent me this AMAZING link: http://tipnut.com/10-homemade-laundry-soap-detergent-recipes/. It is THE most complete information I've ever seen on homemade laundry soap detergent. Check out the FAQ link, and be sure to peruse the comments section for some very useful tips!
I've seen this recipe floating around a few different places, so I'm posting the two I think are the best. I've tried one batch of the dry powdered version and loved it! But it's a little expensive for the way I was using it...
Version #1: Powdered
3 bars (5.5 oz.) Fels Naptha, grated VERY FINELY
3 cups Washing soda (Arm & Hammer)
1 1/2 cup Borax
2. Store in airtight container.
3. Use 2 Tablespoons for normal loads, 3 Tablespoons for heavy loads.
Version #2: Liquid (from the Duggar's new book (that I'm coveting))
1 bar (5.5 oz.) Fels Naptha
1 cup Washing soda (Again, Arm & Hammer makes this)
1/2 cup Borax (I use a full cup)
1. Grate Fels Naptha soap into saucepan. Cover with hot tap water.
2. Cook over medium-low heat, stirring continually, until the soap is completely dissolved.
3. Put washing soda and Borax into a 5-gallon bucket. Pour in the hot (dissolved) soap mixture. Stir well until the powder is dissolved.
4. Fill bucket to the top with hot water. Stir and cover, then allow to sit overnight.
5. NEXT MORNING: Stir mixture.
6. Mix equal amounts of soap and water into a smaller container.
7. Shake before using one cup per load (top loader). Use 1/3 cup for a side-loader.