I used this recipe from The Family Homestead: http://www.thefamilyhomestead.com/laundrysoap.htm. I'll print it briefly below in case the link goes bad in the future.
Homemade Laundry Soap
1/3 bar Fels Naptha or other type of soap, as listed above1/2 cup washing soda(sold in the cleaners aisle, the Arm & Hammer brand is in a yellow box)
1/2 cup Borax powder
2 gallon bucket
Grate the soap and put it in a sauce pan. (I used the lidded stockpot I wanted to keep my detergent in.) Add 6 cups water and heat it until the soap melts. Add the washing soda and the borax and stir until it is dissolved. Remove from heat. Pour 4 cups hot water into the bucket -- I put it in the pot with the soap mixture. If you're using a separate bucket, add soap mixture to the 4 cups of hot water in your bucket and stir. Now add 1 gallon plus 6 cups of water and stir. Let the soap sit for about 24 hours and it will gel. It will not be a solid gel -- it'll be more watery and like Chinese egg drop soup. Use 1/2 cup per load. I dedicated a ladle to this job and it stays in the pot. I sometimes use 1 cup for especially soiled clothing.
I made a few changes. I used a half bar of Fels Naptha, which is sold at Wal-mart. I never knew that because I was never looking for it. I go straight for the orange boxes of Tide. I also bought the Borax at Wal-mart but I had to go to a hardware store for the Washing Soda.
I also left the soap in the stainless steel stockpot I melted the soap in. I just added water to it instead of adding it to a bucket of water.
What do I think of it?
The scent is not objectionable. It cleans well if the laundry has an ordinary amount of soil. Mud and toner stains (my husband repairs copiers) need to soak for a few hours and then they come clean. Red stains like blood, berries and tomatoes need serious pre-treating though. It's no match for blood the way Tide With Bleach is. I like that this detergent is liquid because it will dissolve in cold water almost as well as warm. Powder detergent usually clumped in cold water.
If I hadn't liked it, I would've still used it and its ingredients up -- Fels Naptha can treat stains, Borax and Washing Soda can be added with other detergent. The homemade liquid detergent could've cleaned toilets or tubs. The FlyLady says "soap is soap."
But I like it OK.
That said ...
I miss Tide. Old habits die hard.