How to make your own washing powder | eHow- how to make washing powder lemon washing soap uses washing soap powder ,Fill a large bowl with 2/3 to 3/4 of a gallon of water. Hold a cheese grater or rasp over the bowl and begin grating the soap into the water, stirring to prevent the soap from sticking together.How to Make Homemade Laundry Soap (Liquid or Powder ...May 01, 2019·Instructions. Powder Instructions; Use a cheese grater to grate or shred the bar soap. In a large bowl, mix together the borax, washing soda, and baking soda.