Overflow Tubes
The toilet overflow tube is secured to the base of the toilet and rises to within an inch or two from the top of the toilet tank to allow excess water to drain into the toilet bowl when necessary. Water in the toilet tank should sit approximately ½" below the overflow tube and should be aligned with the fill line along the back of the toilet.
If the water is too high and is spilling into the overflow tube, try lowering the float arm that controls the water level in the tank. If the problem persists, you may need to purchase replacement parts.