Fluidmaster Flush'n Sparkle Self-Cleaning Cartridges. Fluidmaster makes three different cartridges for the Flush'n sparkle Cleaning Kit. They make a Blue Cartridge, Bleach Cartridge, And a Septic Tank Cartridge. The Blue Cartridge is a replacement for the old drop-in tablets. This cartridge cleans with every flush, and helps prevent the spread of viruses and bacteria. The Bleach cartridge is environmentally friendly and cleans with every flush. The Septic Tank Cartridge is to help maintain your septic tank. This cartridge also provides BioBalance, which helps reduce drain field clogging while also cleaning your toilet bowl. Each Pack of comes with two cartridges. Each cartridge can last up to three months.