First, you have to grate the Fels-Naptha soap up. I used a simple box grater and the hubs muscle to make quick work of the bar.
Then, using an old pot that I had in the pantry I melted the grated soap into 4 cups of hot water over Medium Low heat stirring frequently until I was sure there was no lumps of soap left. It took about 5 minutes total.
Then I stirred everything together until all of the powder was dissolved. Then I filled the rest of the 5 gallon bucket up with more hot water and set it aside to cool. Once it was cool I added 40 drops of essential oil to make the whole batch smell like fresh linen. Then I covered it up and let it sit overnight to thicken up. In the morning I stirred the batch and filled a clean, empty laundry soap dispenser 1/2 way full with soap and then filled the rest with water. Just make sure you shake the container before use, because it will gel up a bit.