I wash hair with foot powder and a towel. Takes same amount of time. Use only a little on hands at a time (rub hands together for thin layer), put through hair, do it again a few times. Mess up hair. Then pull the soaked up oils/dirt into towel you pull your hair through.
Works great. Been doing it for years. Figured it out on my own one day when bored. “What if I didn’t use water? How could I do it?” and got here from experimenting.