If you suspect your toilet tank is leaking into the toilet bowl, there are a few possible causes and easy ways to check this problem.
Confirm Your Toilet Tank is Leaking
First, be sure this is what’s actually happening. One of the easiest ways to do this is by putting a few drops of blue food coloring into the water-holding tank. Do not use the toilet for a few hours or overnight if possible. If the water in the bowl is any shade of blue, your tank is leaking.
Another way of knowing that it's leaking is if your toilet runs water into the tank on its own, then stops, and then runs again later.
Investigate Probable Causes
There are a few possible reasons why your toilet tank could be leaking into the bowl. Once you know what is causing the problem, you can take steps to remedy it.
The most common cause of this leakage is a malfunction of the rubber flap at the bottom of the holding tank.
When the rubber flap malfunctions, it doesn’t close tightly enough, and water can start to refill into the holding tank. Oftentimes, the flapper might just be worn.
For a quick fix, try flushing the toilet with the lid off of the holding tank while you hold onto the flapper. Dry it off completely and then apply petroleum jelly to the rubber where it meets the tank opening. This quick fix could help create the seal you need to fix your issue.
If that still doesn’t work, you can replace a faulty toilet flapper yourself by buying a replacement flapper.
Cracks in Holding Tank
If your holding tank is cracked, it may also leak into the bowl. If this is the case, you should replace your toilet right away or call a professional to do so. If the crack continues to split, it could flood your entire house.
Loose Tank-to-Bowl Assembly
Loose bolts that fix the toilet tank to the bowl can cause a leaking toilet tank. If the nuts are loose, tighten them with a wrench. However, be careful not to tighten them too much because the porcelain tank could crack.