Abstract: An emergency valve unit which can be sold as a kit and which can be easily and quickly installed into typical, commercially-available toilets to prevent the bowl of the toilet from overflowing during the flushing thereof. The valve unit has a relatively thin, flat housing which is positioned between the water tank and the stool section of the toilet and is held there by the seam bolts that normally secure the tank to the stool. The housing has an opening therethrough which aligns with and forms a portion of the fluid passage between the tank and the stool. A valve element is slidably mounted in the housing and is manually movable to open or close said opening by means of a rod which extends from said housing. If at any time it appears that the toilet bowl is ready to overflow during a flushing operation, the rod can be pulled to close the valve unit thereby shutting off the flow of water from the tank to the bowl.