1 bar of Fels-Naptha
(This is an old time, heavy duty laundry bar used for stain removal. Any bar soap will work but this is suppose to work the best.)
1 cup of Arm & Hammer Super Washing Soda
1 cup of 20 Mule Team Borax
I found the Fels-Naptha ($1.29 bar) and the Arm & Hammer Super Washing Soda at Ace Hardware. I found the Borax at Wal-Mart.
Shave the bar of soap into small pieces using a cheese grater.
In a large sauce pan, heat a gallon of water to boiling. As soon as the water boils, turn the heat down and add the soap pieces. Stir occasionally until the soap dissolves, then pour the mixture into a clean 5 gallon bucket. Stir in the Borax and washing soda. Fill the bucket the rest of the way with warm water and stir.
Place a lid on the bucket and let it sit overnight.
After 24 hours, you'll have a giant gel clot of detergent. Break it up with your hands, to make it easier to pour out of the bucket.
Use about 3/4 cup of detergent in a regular washing machine and about 1/4 cup in a high efficiency machine.