How do I test to see if water is leaking from the tank into the bowl?

After flushing the toilet, let it refill. Now put a few drops of food coloring into the tank. If the color appears in the bowl after a few minutes, there is a leak.

Check your state and local codes before starting any project. Follow all safety precautions. Information in this document has been furnished by the North American Retail Hardware Association (NRHA) and associated contributors. Every effort has been made to ensure accuracy and safety. Neither NRHA, any contributor nor the retailer can be held responsible for damages or injuries resulting from the use of the information in this document.