So I've been wanting to do this for months and finally took the plunge. It was SO EASY and I'm excited to use it in my laundry. From start to finish the whole process took about 10 minutes.
(All ingredients were purchased at the local Broulim's grocery store.)
Homemade Laundry Soap
1/3 bar Fels-Neptha soap, finely grated
1/2 cup borax
1/2 cup washing soda (not baking soda!)
1 2-gallon bucket (I used an empty Member's Mark laundry detergent container)
A lot of water
Heat six cups of water on the stove with the grated soap until the soap has melted. Add the borax and washing soda; cook and stir until dissolved. Put four cups of hot water in your bucket; add the soap and 22 more cups of water (1 gallon plus 6 cups). Stir. Let sit 24 hours. The texture will gel and be kind of drop-egg-soupy. Use 1/2 cup for a large load of laundry. (You can add 1 oz of essential oils for a scent if you want.)
I haven't double-checked the math on this, but the lady whose website I stole this recipe from claims the cost comes down to $.01 a load.