I've been meaning to make my own laundry soap for a while now and I finally did it.
It was so simple and so cheap. I can't believe I didn't do it sooner.
1 bar Fels-Naptha (I found mine at ACE hardware)
1 cup borax
1 cup washing soda (this is NOT the same as baking soda)
5 gallon bucket
Using a cheese grater, grate the entire bar of soap
Dump your soap into a large pot. Add your borax and washing soda. Cover with enough water to melt the stuff in (used a gallon but you could use less if you have a smaller pot.)
Heat up your mixture and continue stirring until your soap is dissolved.
Dump you mixture into your 5 gallon bucket and fill up the rest of the bucket with water.
Put your lid on you bucket and let it sit for 24 hours.
I poured some into an empty detergent container to make it easier to pour.
I use 1 cup per load and my clothes come out just as clean as with the store bought stuff.