This economy size 12.5kg (or 26.4lbs) bucket of sodium phosphate tribasic (or trisodium phosphate) is white, granular, and highly soluble in water. It is commonly used in varying strength solutions for cleaning and degreasing. It is also used to degloss walls prior to painting, for wallpaper removal and driveway cleaning.
A well presented short video succinctly describing and demonstrating uses of the chemical is recommended viewing: http://youtu.be/kxiUOtVCluU