nicktheplumber
Toilets are pretty simple devices, but you need to understand how they work to troubleshoot problems. Common residential toilets consist of two main parts: 1) a tank, that holds a couple of gallons of water; and 2) a bowl, which holds a smaller amount of water and maintains a trap water seal. The tank is connected to a cold water supply and uses a float valve to maintain a level of water needed to “flush” the bowl. The tank is connected directly to the bowl and water is sent to the bowl by opening the “flush valve.” The flushing action depends upon gravity. In some toilets, usually in commercial applications, the tank is dispensed with and flushing is accomplished by a high-flow high pressure water supply.
If you understand the way toilets work, you can logically diagnose their problems. A falling water level in the tank has to be due to a leaking flush valve or some other leak from the tank (either a crack or a leaky connection to the tank). If there is a crack in the tank, you’d expect to find water leaking onto the floor. One way to check for a leaky flush valve is to put a dye in the tank and see if that dye enters the bowl (when you don’t flush it).
A falling water level in the bowl can be due to a cracked bowl. Again, you’d expect to see water leaking onto the floor or subfloor. Putting dye into the bowl may help identify such leaks.
There are some other ways water can drain from the bowl without a crack in the bowl itself. All of these other ways involve what is called “siphonage.” The two most common causes of this are: 1) faulty toilet venting; and, 2) a partial blockage in the toilet trap caused by something (such as a rag) that wicks water out of the bowl. This can usually be fixed by using a closet auger.
