Valued for their soft texture, Kleenex and other facial tissues are at hand's reach in most homes. They are often used interchangeably with toilet paper during cold and allergy season, to catch sneezes and dry runny noses, but they're not good for the potty. Facial tissues do not break down in water the same way toilet paper does. They should never be flushed down the toilet; flushed Kleenex can cause clogs and other serious plumbing issues.
Flushing Kleenex and other non-toilet-paper materials down a toilet can clog the toilet itself, but more commonly it creates significant clogging in the home's main drain pipe leading to the sewer or septic system. Because the tissue material is resistant to breaking down, it gets stuck on bends or other debris in the drain pipe, contributing to the stoppage. Flushed tissues are a common source of problems for municipal sewer systems. For homes with septic service, tissues can create a need for more frequent pumping of the tank.