The City of Hillsboro, Ohio

This is caused by the fill tube being pushed too far down the overflow tube. When the end of the fill tube is pushed below the water level in the tank it will sometimes cause a siphoning effect.

The way to determine this is to take a flashlight and look directly down the overflow tube. If you see the water running or dripping from the end of the filler tube, then the siphoning effect is taking place. This is very easy to correct. Pull the filler tube up so that the end of the filler tube is above water level in the tank. If the filler tube is too long and it is made out of rubber snip the excess off with a pair of scissors.