Fluidmaster Flush'n Sparkle Self-Cleaning Kit. This kit puts the cleaning solution directly into the overflow tube of the flush valve. No chemicals ever touch the parts inside your toilet. This kit is a great replacement for Drop-in tablets. Chemicals in drop-tablets deteriorate rubber parts inside the tank. These parts can include the flapper and other rubber parts. Using drop-in tablets over time can have costly repair and parts cost. This kit provides a cleaning solution with out having the costly repairs that come with the drop-in tablets. This kit includes a blue cleaning cartridge, or you can choose in the pull down for the Bleach Cleaning cartridge. Cartridges can last up to 3 months.