How to Fix a Leaking Toilet Tank-to-Bowl Gasket

Begin by preparing your work area. Lay old towels on the floor around the base of the toilet to absorb any spilled water. Locate the water supply shut-off valve, typically on the wall behind the toilet, and turn the handle fully clockwise until it stops. This will cut off the water supply. Next, flush the toilet to empty as much water as possible from the tank. Since some water will remain at the bottom, use a large sponge or absorbent towel to soak it all up and wring it into a bucket. The tank must be completely empty before you proceed.

Locate the water supply line, which is the flexible hose connecting the shut-off valve to the toilet tank. At the point where it connects to the tank, there is a large coupling nut. Using an adjustable wrench or channel-lock pliers, grip this nut and turn it counter-clockwise to loosen and remove it from the fill valve's threaded shank. Have a small towel ready as a small amount of water may drip out.

Look underneath the rim of the toilet bowl where the tank sits. You will see the ends of two (or sometimes three) bolts with nuts on them. To remove these, you need to prevent the bolt from spinning inside the tank while you turn the nut below. Use a screwdriver (usually a flat-head) to hold the bolt head stationary inside the tank. With your other hand, use a deep socket wrench or an adjustable wrench to turn the nut counter-clockwise. If the bolts are severely rusted and won't budge, your best option is to use a mini-hacksaw to carefully cut through each bolt in the space between the tank and the bowl.

Once the water line and all mounting bolts are removed, the tank is free. Grip the tank firmly on both sides and lift it straight up and away from the toilet bowl. Be mindful that it might be slightly heavier than anticipated. Carefully carry it to the prepared area on the floor and gently set it down on its back on top of the old towels to protect both the tank and the floor.

With the tank resting on its back, you can see the large, old tank-to-bowl gasket (also called a spud washer) around the flush valve assembly. Pull this gasket off. If there are any remaining old bolt heads inside the tank, remove them. Thoroughly clean the area on the bottom of the tank around the flush valve opening, as well as the corresponding surface on top of the toilet bowl, using a putty knife or scraper to remove any old, dried gasket material. Insert the new bolts from your kit through the holes from inside the tank, making sure the new rubber washers are on the inside to create a seal. Finally, press the new, large tank-to-bowl gasket onto the flush valve threads on the outside of the tank. Ensure the tapered side of the gasket faces down, away from the tank, as this side will fit into the opening on the bowl.

Carefully lift the tank, holding it level, and position it back onto the toilet bowl. Look from the side to guide the newly installed bolts through the corresponding holes in the bowl's rim. Lower the tank slowly until the new gasket rests evenly on the bowl's water inlet. From underneath, install the washers and nuts onto the bolts. The order is typically metal washer, then rubber washer, then nut, but check your kit's instructions. Hand-tighten the nuts first. Then, using a wrench, tighten each nut a little at a time, alternating between them to ensure the tank is pulled down evenly and without stress. Continue until the tank is stable and does not rock.

Reconnect the water supply line's coupling nut to the fill valve shank on the bottom of the tank. Screw it on by hand until it is snug, then give it a final quarter-turn with your adjustable wrench. Now, slowly turn the water shut-off valve counter-clockwise to allow water back into the tank. As the tank fills, vigilantly inspect all your new connections: the supply line nut, the base of the new tank bolts underneath the bowl, and the entire seam between the tank and bowl. Once the tank is full and the water stops, flush the toilet several times. After each flush, thoroughly check all connection points for any signs of water. Using a dry paper towel to wipe these areas makes it easy to spot even the tiniest leak.