There are a number of signs that a toilet needs some repairs, but many toilets leak without conspicuous indications of trouble. Here are some of the more obvious signs of a leaking toilet:
*** Any sounds coming from a toilet that is not being used are sure signs of leaks.
*** If you have to jiggle the handle to make a toilet stop running.
*** If you have to hold the handle down to allow the tank to empty. This can also mean the chain or strap is too long and doesn't lift the flapper or ball high enough to float on its own.
*** If water drips out of the refill tube into the overflow pipe. (also under the lid)
*** If a toilet turns the water on for 15 seconds or so without you touching the handle, this is otherwise known as the phantom flusher.
However, even if your toilet doesn't have any of these symptoms, it's still possible that it is leaking. These leaks are known as SILENT LEAKS, because they usually go undetected. There is an easy test you can do that will positively tell you whether or not your toilet is leaking. And if the test shows that the toilet is leaking, there is a second test that tells you what part inside the tank is responsible and needs fixing.
Remove the cover on the toilet tank and carefully set it aside so it can't be accidently knocked over and cracked. Take off the lid of the tank and if you see water running over the top of the overflow tube, you definitely have a leaking refill valve. (or the float is out of adjustment) If you are unsure whether or not water is running over the top of the overflow pipe; sprinkle talcum powder on top of the water in the tank, and you can clearly see whether or not it is.
Remove any "in-tank" bowl cleaners that color the water and begin the test with clear water in the tank as well as in the bowl. You'll need some dye. Food coloring or instant coffee works fine. Wait 30 minutes and make sure nobody uses the toilet. In 30 minutes if you find any of the dyed water is now in the toilet bowl -- your toilet is leaking. A properly operating toilet will store water in the tank indefinitely without any water running into the bowl.
So for now, let's say you've done the dye test and found your toilet is leaking, you now have to find out which part is the culprit...the flush valve (flapper at the bottom of the tank) or the refill valve.
The Pencil Test. Draw a pencil line on the back wall of the tank on the inside of the tank at the waterline. Then turn the water supply off, either under the tank or at the main shutoff~wait 20-30 minutes. If the water level remains at the pencil mark ~~ the leak is occuring at the REFILL VALVE, the unit in the left side of the tank. If the water level falls below the pencil mark ~~the leak is in the FLUSH VALVE, the unit located in the center bottom of the tank.