Use a grater and grate the entire bar of soap.
Place the grated soap in a large pot. Pour in enough warm water to completely cover the soap. Bring heat to medium and completely melt the soap. Stir as needed.
In your bucket (I actually used a 4 gallon bucket that my pool chemicals come in. It has a lid)
add the washing soda and the Borax and SLOWLY fill with hot water. Stirring continuously to dissolve. NOTE: Leave enough room in the bucket to add the soap later.
Add the soap and continue to stir until all is well mixed. You may need to come back and stir every hour so it won't solidfy too much.
The consistency is like a jello. I keep mine in the bucket I mixed it in, but after a couple of days and the mixture completely cools you can re-package if you'd like.
I have a front loading washer so I use about 3/4 cup of the detergent. If you have a top -loader I would put the detergent in and let the water help to dissolve it before adding the clothes. Using 3/4 - 1 cup of the detergent.
If you have any questions, feel free to e-mail me or ask in the comments. It was a messy process to put together, but I'm happy with it and will continue to make this as I run low in the future. Great money saver.