The *Sloan Flushmate C-100500-K Flush Valve Cartridge* is used on all Sloan Flushmate Series EXCEPT for the 200 Series. This Sloan Flushmate cartridge threads into the pressure vessel. When you press the flush handle on the toilet, the linkage rod depresses the cartridge. When the cartridge is depressed, it starts the flush cycle by letting the pressurized water out of the vessel and into the toilet bowl.