For 5 gallons - (just noticed I typed a gallon above oops)

Grated bar of Fels Naptha dissolved into 4 cups hot water, put in pot, heat on medium until it dissolves all the way, 10-15 minutes.

Fill bucket halfway with hot water and stir in the soap mix, 1 cup borax, and 1 cup of washing soda. I don't add essential oils to scent mine but you can, doesn't take much.

If the bucket isn't full I top it off. Stir until it's all mixed. I want a dedicated stick blender for this but am cheap.

After about 24 hours it sets up to a gloppy gel unless it's really warm. I use 1/2 cup so that's 160 loads.

Next batch is still on my to-do list, ran out of energy that day.