A toilet tank that does not remain filled can occur from a broken flush mechanism or an improperly balanced tank. A broken flush mechanism will fail to fill the tank properly when the toilet is flushed or will continuously fill the tank. An unbalanced tank will continuously fill and drain into the toilet. The first step in repairing the tank involves diagnosing the problem. Repair or replacement of any part of the tank only takes about 30 minutes.
Set a level on the toilet tank and check for level from left to right and front to back. Any indication of the tank being unlevel in either direction will cause the toilet to fill continuously. Skip to Step 4 if the tank is level.
Turn the water off to the tank and drain out all the water by flushing the toilet. Unscrew the retaining bolts connecting the tank to the toilet with an adjustable wrench holding the nuts from beneath and a screwdriver unscrewing the bolts from inside the tank.
Lift the tank up slightly and add rubber washers to the left or right bolt as necessary to obtain a level tank. The washers will sit between the tank and the toilet. Set one washer at a time, reinstall the retaining screws, and test the level of the tank. Add additional washers as necessary until the tank is properly levelled. Tighten the retaining nuts down with an adjustable wrench.
Lift the float straight up with the lid to the tank removed. Lifting the float will stop the water flow in a functioning fill valve. Monitor the flow of the water if lifting the float stops the water. Replace the tank hardware if lifting the float does not stop the flow of water.
Press down on the tank stopper, the rubber connection covering the drain, and monitor the tank. The water should stop filling on its own without having to lift the float. Replace the stopper if the tank functions properly by holding down the stopper.
Turn the water off and drain the toilet by flushing it. Unscrew the fill hose from the base of the tank and remove the retaining nut holding the fill pipe in place with an adjustable wrench. The nut on the base of the tank holds the fill pipe in place. Lift the pipe out of the tank and insert a new one into the hole with a rubber washer on the pipe in the tank and one on the pipe beneath the tank. Tighten the nut down and reattach the water line. Test the tank for proper function.
Unbolt the retaining nuts and screws holding the tank to the bowl with the water drained out of the tank. Lift the tank free of the toilet and unscrew the retaining nut that holds the stopper down. The nut is beneath the rubber grommet sitting between the tank and bowl. The nut unscrews by hand or with an adjustable wrench. Remove the old stopper and overflow tube, which are one piece, and install a new one. Reattach the retaining nut and rubber grommet. Reinstall the tank to the bowl and attach the water lines. Test the tank for proper function.
Replacement fill tubes and stoppers come with explicit instructions on the installation of the units and are relatively cheap. The process may seem complicated but is relatively easy once you look at the components. Take your time and remember that each connection has a rubber washer inside the tank and beneath the tank.