Pros know that acids are required to dissolve soils, hard water buildup, and rust in toilets. This professional grade acidic formula clings longer to remove stains with less scrubbing, leaving a fresh winter green fragrance.Works Fast: Quickly removes rust, dissolves organic stains, and eliminates hard water residueEasy to Apply: Angled neck makes under-the-rim application easy, while thick gel formula clings to vertical surfacesPowerful Formula: Strong 10 percent acid gel formulaFor use on: Toilet bowls and urinals, safe for septic tanks, drain lines, and water treatment systemsNot for use on: sinks, bathtubs, countertops, floors or any enameled surfaces