Gel Scrub Foaming Acid Tub and Tile Cleaner removes soap scum buildup and hard water deposits. Use Gel Scrub on tubs, sinks, floors, walls, shower stalls, toilet bowls, urinals and any other hard, nonporous surfaces on which acid can be safely used. Gel Scrub is also an excellent grout cleaner. Use Gel Scrub at full strength or diluted at 1:10.