One way to see if water is seeping from the tank is to conduct a simple dye test. Use food coloring or a powdered drink mix to noticeably color the water in the toilet tank.
1. Remove any sanitizing products from your toilet that may color the water.
2. Place the coloring agent in the tank.
3. The tank water will change color, while the toilet bowl water should be clear.
4. Wait ten minutes.
5. Check to see if any coloration appears in the bowl. If so, then you have a leaking flapper valve.