Using a standard sized measuring cup, take ¼ cup of liquid castile and pour it into a large mixing bowl.
Measure one cup each of baking soda and washing soda and add it to the liquid castile soap.
Mix the dry ingredients well with a long-tailed plastic spoon or stirrer.
Slowly and gradually add one cup of white vinegar into the dry mixture and combine it well. If you add all the vinegar at once, the mixture will become foamy.
Stir the mixture well to get vinegar and the dry ingredients all mixed up completely. You can also use a whisk to mix the items.
Your mixture may become a bit lumpy; if so, mush them up with hands. It is recommended you wear plastic gloves when breaking the lumps, but even if you don’t wear the gloves, this mixture is not going to corrode your hands.
Once your mixture has turned into a smooth paste, let it sit for several minutes (5 to 10 minutes).
After some time you will notice that your soap has soaked up all the vinegar and has turned into a thick lumpy paste.
Boil one cup of water in a sauce pan and add it to the thick soap paste. Boiling water will melt down any remaining lumps, making it easy for you to mix the hardened concoction.
Whisk the mixture well and transfer it to a jar with a tight lid.