When most people go to the bathroom they're not thinking about how the toilet flushes. They just expect and hope that it will. But there's a slightly complicated system going into motion every time you flush the handle. The most important part in this system is the flush valve, of which there are several types.
When it comes to flush valves, size does matter. However, there are only two main sizes to consider. Most newer toilets use a 4-inch flush valve, which is slightly larger than the 3-inch flush valve used on most older toilets. The size relates to the diameter of the valve itself. You can use only a 4-inch flapper on a newer toilet with a 4-inch valve hole, and vice versa. The older flush valves are used only for older toilets.
Adjustable Flush Valves
Many flush valves are adjustable. They contain an adjustable part so you can improve your toilet performance. Most flappers have a chain or plastic cord that attaches to the lift rod attached to the handle. Shorten the length of this chain or cord, and the flapper lifts up faster or slower when the flush handle is depressed. It's a way to control how fast the toilet operates in low or high water pressure buildings.
Attached to Overflow Tube
Some flush valves attach to the overflow tube, which is a vertical tube in the centre of the toilet tank with a hole at the top. If water reaches the hole, it drains down through the tube to avoid overflows. Some flappers have plastic rings that fit over this tube, while others hook onto a base that slides down over the tube. It depends on which type of flush valve you want to use and which works better in your toilet.
Alternative Flush Valves
Some flush valves are made specifically for certain types of toilets. Kohler, for instance, has flush valves that only fit its toilets. This is a proprietary part and it won't work on other brands. Another type of flush valve has no float ball. It contains a floating ring right on the overflow tube, along with a plastic rubber flush valve. The complete unit is easy to install because it saves the step of putting on a new float ball.