When a running toilet “ghost flushes” at intervals greater than 15 minutes apart, chances are the tank-to-bowl gasket needs to be replaced.
Replacing the tank-to-bowl gasket is usually done in conjunction with replacement of the flush valve. If the flush valve is functioning properly, replacing just the tank-to-bowl gasket should fix the problem.
Step 1: Turn off the water supply to the toilet and flush the toilet to remove most of the water in the tank.
Step 2: Place a towel beneath the toilet tank and unscrew the supply line from the fill valve.
Step 3: Remove the tank lid and place it in a safe place.
Step 4: Use a screwdriver and a closed-end box wrench to remove the nuts from the tank bolts on the underside of the tank and stool.
Step 5: Lift the tank from the stool and dump out the excess water inside the tank.
Step 6: Lay the tank on its side and use a large pair of groove joint pliers to remove the flush valve nut holding the tank-to-bowl gasket in place. If a large pair of groove joint pliers is not available, remove the nut by positioning a flathead screwdriver on one of the corner edges of the flush valve nut and hit the end of the screwdriver with a hammer to loosen the nut.
Step 7: Remove the old tank-to-bowl gasket and replace it with a new gasket.
Step 8: Place a paper gasket atop the tank-to-bowl gasket and hand tighten the flush valve nut into place.
Step 9: Once the nut is secure, use groove joint pliers or a hammer-screwdriver combination to tighten the nut at least another quarter of a turn. Overtightening the nut could crack the porcelain tank, but a loose nut will cause water to continue to seep out of the tank and into the stool.
Step 10: Position the tank onto the back of the stool and hand tighten the nuts onto the tank bolts.
Step 11: Place a level across the tank to assure the tank is level as the nuts are tightened. Continue to tighten the nuts with a closed-end box wrench, alternating between nuts until the tank is secure.
Step 12: Reattach the supply line, turn the water supply on and check for leaks. Give the toilet a quick flush to assure everything is working properly.