The sound of small bubbles inside the toilet tank gets quickly annoying, and you can often hear it even with the lid on the tank. The bubbles are the result of a malfunction of the filling valve, which has the duty to allow the water in the tank after each discharge. The repair usually involves the replacement of a gasket of the filling valve or replacement of the filling valve itself.
Gerber Plumbing VP-21-528 Gerber Viper Watersense High-Efficiency Elongated Siphon Jet Toilet Bowl, Ada-Compliant, 1.6 Gpf/1.28 Gpf, White - 2463449
Locating the filling valve
Remove the lid of the toilet tank and look down on the tank, and you will find the fill valve on the left side. Below the tank, the feed line is connected to the bottom of the fill valve, partially protruding through the bottom of the tank. This is where the water moves up from the supply tube and enters the tank. Locate the shut-off valve on the opposite end of the tank supply line, either on the wall or bathroom floor. This valve controls the pressure of the water that enters the tank and also allows it to close completely out of the water that goes to the tank.
Testing the problem
With the tank lid turned off, you can lower the water pressure and see if this prevents the bubbles in the tank. Slightly turn the shut-off valve to the right to decrease the pressure. Sometimes this stops the bubbles, especially if the bubbles are entering the tank from a point around the base of the filling valve. If this does not prevent the bubbles, press down on the rubber gasket inside the tank and determine if the bubbles stop. Sometimes, the fin may not sit properly and allow some water to escape to the bottom of the vessel. This can possibly cause the bubbles, but it is not the most likely cause. Checking anyway allows you to conclusively discard it out.
Repair of the filling valve
If the fill valve is a float valve assembly, pull up slightly on the long arm of the float valve, raising the ball float at the end of the boom. This can temporarily stop the bubbles, although you may have to take additional measures. Turn the stopcock completely to the right, pull the chain and absorb all the water from the leftover tank with a bath towel. Disconnect the supply line from the bottom of the fill valve, lift the tank fill valve and replace the rubber washer on the bottom of the fill valve between the valve and the hole in the tank. Install the fill valve in its place, reconnect the water line, turn the stopcock to the left and see if a new washing machine prevents bubbles.
Replacing the filling valve
If you are replacing the washer in the base of the fill valve, do not remove tiny bubbles, replace the fill valve with a new one. Follow the same procedure as you would to replace only the washing machine, only this time install a new valve. If your toilet currently has a float valve assembly, consider installing a newer-style float-cup filling valve, which allows for fewer problems, especially with no float ball or arm to treat. The only tool that should be necessary for replacing the washer or the fill valve is an adjustable wrench to loosen and tighten the nut that connects the supply line to the bottom of the fill valve.