Repair toilets that leak from the tank when flushed by replacing the large, rubber tank-to-bowl washer. For tanks that leak constantly, the problem could be a loose connecting bolt, ridge on the porcelain or worn rubber bolt washer. If it is necessary to remove the tank from the bowl, replace both the tank-to-bowl and bolt washers.
If a constant leak is a problem, begin the process by tightening each of the connecting bolts another one-quarter turn. Avoid overtightening these bolts to prevent breaking the porcelain. If tightening the bolts doesn't fix the problem, remove the tank and replace the washers.
Before removing the bowl, turn off the water to the toilet using the supply line valve. Flush the toilet and hold the handle down to remove as much water from the tank as possible. Use a sponge and bucket to remove the remainder of the water.
Use an adjustable wrench to remove the supply line from the bottom of the tank. Loosen the connecting bolts and remove the tank from the bowl. Remove the old washers and inspect the porcelain around the holes for chips or cracks. If the tank is cracked, it requires replacement. If there are ridges around the hole, use a file or sandpaper to smooth them. Install the new washers and replace the tank on the bowl. Tighten the bolts in an alternating pattern to prevent cracking the tank.