Turn the shutoff valve that controls the water flow to the toilet. The shutoff valve is located on the back wall behind the toilet. It is usually located on the left side of the toilet as you are facing it, but it can also be located on the right side. Turn the shut off valve clockwise or to the right to shut off the water.
Flush the toilet to drain the water out of the tank. With the water shut off the tank will not refill. There will still be some water left in the tank after you flush it.
Place a bucket underneath the waterline inlet connected to the underneath side of the tank. The inlet is on the left side of the tank as you are facing it. Loosen the waterline retaining nut connected to the threaded nipple on the underneath side of the tank. As you loosen the nut, remaining water in the tank will begin flowing out; hold the bucket near the valve to catch the water. Continue loosening the retaining nut until you can pull the waterline off of the tank (Reference 1).
Loosen and remove the retaining nut and washer that is also located on the threaded nipple on the underneath side of the tank. The retaining nut and washer are holding the Flowmaster fill valve in place inside of the tank. You may need to hold on to the fill valve with one hand while you loosen the nut with the other hand to keep the fill valve from turning.
Remove the fill tube that is running from the Flowmaster to the overflow drain. It is held in place by a clip. Lift the old Flowmaster out of the tank.
Hold the new Flowmaster fill valve next to the old fill valve to match the height. Twist the base of the new valve to the right to make it shorter, or to the left to make it longer.
Place a washer on the end of the new Flowmaster. Set the new Flowmaster fill valve in the same position from where you removed the old fill valve. Slide the second washer on the threaded nipple on the underneath side of the tank. Place the retaining ring onto the threaded nipple and turn it clockwise to tighten it. Clip the water tube to the overflow drain inside of the tank.
Reconnect your waterline and turn the water shutoff valve back on to allow your tank to fill.