One way to figure out if your toilet is not working properly is to put some food coloring into the tank. If the coloring leaks into the bowl then your toilet needs to be serviced.
The most common item that needs to be fixed on a toilet is the Flapper. Most people think that when replacing a flapper it’s a “ONE SIZE FITS ALL”. That is not necessarily correct. All manufactures have different flappers for different models of their toilets. Take for example Kohler. They have a different flapper for every model of toilet they manufacture. Some universal flappers fit but will do not work correctly. If you are not sure which flapper you need for your toilet, call the manufacture or your local plumber. They will be able to find the correct flapper to fit your toilet.
If you’re in the market for a good toilet we recommend the Gerber Viper – Elongated High Performance Toilet. The best toilet for the price.