Fluidmaster's Flush 'n Sparkle cleaning system refill cartridges in blue are designed for simple and effective hands-free cleaning for most any toilet. The Flush 'n Sparkle cleaning system refill cartridges in blue puts a powerful blue cleaning solution directly into the overflow tube of the flush valve, so no chemicals ever touch the flapper, fill valve or other toilet tank parts. This prevents the damage that drop-in tablets normally inflict, leading to deterioration and part malfunction. Relax, let your toilet clean itself and eliminate scrubbing. The Flush 'n Sparkle cleaning system refill cartridges in blue offer the same powerful toilet cleaning solution in a 2-pack for up to 6 months of hands-free cleaning on 2 household toilets.