Grate 1/3 of a bar of Fels Naptha laundry bar soap.
Melt the grated Fels Naptha with 6 cups of water in a pan, then add 1/2 cup of Arm and Hammer Washing Soda, and 1/2 cup of 20 Mule Team Borax, stir until dissolved then remove from heat. Pour 4 cups of hot water into a bucket, add the soap mixture and stir well. Then add 1 gallon, plus 6 cups of water to the mixture.
Let the soap sit for 24 hours, it will somewhat gel. Use 1/2 cup per load of laundry. Store the laundry soap in an empty laundry jug. Just think you will never have to recycle or throw away another large plastic laundry jug instead you can reuse the one you have! Total time to make this concoction - 20 minutes. I found this recipe at http://www.thefamilyhomestead.com/laundrysoap.htm there you will also find the calculations used to figure the cost per load - approximately 1 cent!!!
July 7, 2010 - Update on Homemade Laundry Soap
I have used the soap for almost two weeks and I have been pleased with it's performance. Clothing is clean, smells fresh, and no one has complained about any skin irritation. I have adjusted the amount used per load of laundry to 1/4 cup because we have a front load washer that uses less water per load.