The Complete Handbook of Toilet Tanks

Chapter 1: Understanding Toilet Tanks

A toilet tank is a storage vessel and a timing mechanism. It holds water under atmospheric pressure, and when you press the handle, it releases that water into the bowl in a specific volume and at a specific rate to initiate a siphon. That is its entire job. Every repair, every specification, and every purchase decision in this book traces back to that simple function. Understand the storage and the timing, and you understand the tank.

Consider what happens in a typical residential flush. The tank holds about six liters, or 1.6 gallons, of water. The bowl below it also holds water, and the trapway behind the bowl is an S-shaped pipe. When you flush, the tank dumps its contents into the bowl rapidly. The bowl fills past the top of the trapway, and water begins to flow down the far side. Once that flow starts, it creates a siphon, pulling the rest of the bowl contents, waste and all, down through the trap. The tank's job is to provide enough water, quickly enough, to start and sustain that siphon long enough to clear the bowl. If the tank delivers too little water, or delivers it too slowly, the siphon never fully develops and you get a weak flush. If it delivers too much, you are wasting water with every use.

The internal mechanism that controls this release is simple, and it has not changed fundamentally in over a century. You have a flush valve,