Toilet Operation

• Normally, when you press the toilet’s handle on the tank, it pulls on a flapper valve that covers a large drain hole in the bottom of the tank. The water rushes down the drain and into the bowl through a series of small holes under the rim. The sudden introduction of the water from the tank pushes the water in the bowl up and over the curving section of the drain line in the base of the toilet, allowing the water to flow down into the drainpipe in the floor.
  
  

Bowl Water Level

• During normal operation, the water level in the toilet bowl remains constant in between flushes. If you do not use the toilet for an extended period of time, the water in the bowl evaporates and the water level drops. If the water level does not stay the same in between flushes and you use the toilet on a regular basis, then the toilet bowl has a leak.
  
  

Siphoning

• The dropping water level in the toilet’s bowl may be from siphoning in the drain line, caused by a partial clog of toilet paper in the curving section of the drain. If the toilet paper clog drapes over the curving section of the drain line to where the line points straight downward, the toilet paper may siphon the water from the curving section to the straight section of the drain line. Use a flashlight and a small mirror to look for the presence of a clog in the curving section of the toilet’s drain line. If you see any toilet paper, use a plunger to exert pressure on the clog and dislodge it.
  
  

Other Causes

• The toilet bowl’s water level may drop between flushes from other causes, but none of them involve the water leaking into the waste pipe in the floor. Cracks in the toilet’s base, especially near the curving section of the drain line, allow the water to escape the bowl. If you find cracks in the toilet’s bowl, you must replace the toilet. If you have a dog in your house, another possibility for the drop in the toilet bowl’s water level is that the dog is drinking out of the toilet.