Duck Blue Plus are the only automatic toilet freshener with a unique Spring Fresh™ fragrance that freshens your bowl as it cleans with a special foaming formula that works to keep toilet bowl looking clean. It is easy to use and safe on plumbing and septic tanks. Duck Blue In-Cistern has a powerful cleaning action that hygienically cleans your toilet, removes germs, freshens and blues, leaving your toilet clean and fresh throughout, from top to bottom.