A book about two people who had time‐traveled to the late 1700s contained this bit of dialogue: "What do you miss most about our time?" he asked. The woman thought for a moment, then gave the most honest answer she had. "Toilets that flush."
Who doesn't identify with that sentiment? The engineering marvel known as the flush toilet is arguably the fixture in a home that is most underrated and most taken advantage of — and the most missed when you don't have one (or you have one that isn't working properly).
What makes it all work is the flush valve, the part inside the tank that allows water to move inside the bowl. Essentially, after being triggered by the handle or button, the flush valve is what makes the flush happen.
The basic types of flush valves are flapper style (the standard in most toilets), ball style (not used as much these days, but they are still out there), diaphragm or flushometer (used most often in commercial buildings), and the canister‐style.
Regardless of the type, the flush valve's job is to allow water to go from the tank to the bowl in a way that will cause a complete flushing cycle: cleaning the bowl and removing its contents. It then replenishes the trap seal, which puts a certain amount of water in the bowl. (Incidentally, the trap seal is an especially important step, as it keeps the smells — sewer gasses and odors — on the other side of the trap seal. In all truth, this is what allowed us to bring toilets into the house.)
The specific type of flush valve a toilet contains depends on how it was designed, and whatever it was created with is what it uses. In other words, you can't upgrade your toilet from a flapper to a canister‐style. This is important to know when picking out a new toilet.
A canister‐style flush valve lets more water in more quickly than the others, which has its advantages and disadvantages. The faster you get the water into the bowl, the more power it has to clean. Unfortunately, this can also waste water. In some areas around the country, the device might require a larger pipe than standard flush systems, which can mean added expense. Check with your jurisdiction's building department to be sure about local plumbing codes.
Canister‐style flush valves were originally designed for one‐piece toilets, though now they're used in one‐ and two‐piece toilets. They've been around since the 1930s. Those older versions were more expensive, as they were made of brass and the seal holding the water in was made of leather.
Specific steps in replacing the canister‐style flush valve differs depending on whether the toilet is a one‐piece or two‐piece.