Repairing a Leaking Toilet Tank
If the fill valve is leaking turn off the water supply valve. Flush the toilet. Disconnect the supply line from the tank and sponge the inside of the tank until it is dry. Use 2 adjustable wrenches to remove the fill valve. Remove the old fill gasket. If you are not replacing other parts, install the new fill valve and gasket. Turn on the supply line and check for leaks. If necessary, tighten a quarter-turn. Otherwise if the tank is leaking: A screwdriver and adjustable wrench will remove the most tank bolts. Remove the tank bolt, nut, and gasket. Clean the bolt and nut with white vinegar and a small wire brush. If you are not replacing the spud washer, reinstall bolts and nuts with new gaskets. Alternate the tightening of the nuts to evenly draw the tank tight. If you need to replace the spud washer well this is what you would need to do.
If the spud washer is leaking remove the bolts and lift the tank straight up and off the toilet base to remove it. Make sure you have a helper; toilet tanks are usually in an awkward place and heavier than they appear to look. Set the tank upside down on the ground. It is best to set it on something like cloth or rags due to the water still in it.
Replace the spud washer. Take the spud washer to your local store to find the correct replacement. Place a new spud washer over the flush valve tailpiece. Lower the tank onto the base so the tank bolts go through the holes. Reinstall the tank bolts, gaskets, and nuts. Alternate tightening the nuts so they tighten evenly. Reinstall the supply tube coupling and fill valve. Turn on the water supply to check for leaks.
