2 cups grated soap (I make my own, but I used to use a mixture of Fels-Naptha and Ivory. Fels-Naptha is a hard laundry bar and Ivory is cheap and soft, which makes it easy to grate. Fels-Naptha can be found in the laundry isle at a lot of the big stores like Target, Walmart, Cub, etc.)
1 cup washing soda (This is an all-natural product--Sodium Carbonate, but is different from baking soda--Sodium Bicarbonate. You should be able to find it in the laundry isle. Arm & Hammer is the most common brand.)
1 cup borax (This is an all-natural detergent that can also be found in the laundry isle. Some have objections as to whether it's safe or not. This blog post pulls together a lot of what the experts have to say about that. 20 Mule Team is a good brand.)
I grate my soap using a cheese grater. Since it's soap, and I make my own, I use my cheese grater from the kitchen. I figure it just makes it cleaner. Mix all of the ingredients together until the grated soap breaks down a bit and you have a powder-like consistency. Store in an airtight container.
Use 2 tbs for a full load. I use white vinegar as a fabric softener. I pour about a 1/4 cup into my Downy Ball and throw it into the load. (The fabric softener spot on your washer will also work, but your washer may consistently smell like vinegar).
I find that the detergent works great! Whenever I wash whites or really dirty things, I pour a little extra borax in the load and let them soak a bit. They brighten right up!