The Duggar Family recipe for homemade liquid laundry soap includes 4 cups of hot tap water, one Fels-Naptha soap bar, 1 cup of Arm & Hammer Super Washing Soda, and 1/2 cup of borax. Fels-Naptha soap and Arm & Hammer Super Washing Soda are typically available at Wal-Mart.
Grind the Fels-Naptha soap, and sprinkle it into a clean pan on medium-low heat. Stir until the soap has melted. Mix the melted soap in with the borax, water and baking soda. Stir until all ingredients are mixed and indistinguishable. Cover the mixing container with plastic wrap or a cloth, and let it sit overnight to thicken.
The next day, stir the mixture again for good measure. Then fill a used, clean, laundry soap dispenser half full with the soap mixture and half full with hot water. Shake vigorously to mix them. This results in a translucent gel-like mixture, which must cool for a few minutes. Repeat this process until all the soap has been used. Altogether, there should be about 10 gallons when finished.
As an extra option, add 10 to 15 drops of essential oil for each 2 gallons of the mixture after it has cooled. For a less bland scent, lavender, rosemary and tea tree oil are nice additions.