How to Change a Toilet’s Spud Gasket

Originally posted on Men's Journal | By Max Winters | Last updated Jun 4, 2024 7:00 AM ET

Diagnosing a toilet leak? There's a rubber gasket that sits between a toilet tank and the bowl called a spud gasket. It works with the flapper valve to control the flow of water between holding tank and any standard toilet bowl. While replacing a worn out flapper is easy enough, replacing a tank-to-bowl gasket takes a little more work. Leaking toilet water can cause a constantly running toilet, hundreds of gallons wasted, a real mess of your bathroom flooring, and if left unaddressed, even structural damage. Luckily it's an inexpensive seal to fix and it's really just taking something apart and putting it back together.

Signs That the Gasket Needs to Be Replaced

It Fails The Dye Test: To check your toilet for leaks, put a few drops of food coloring into the water tank. Wait 30-45 minutes. If the water in the toilet bowl has changed color, it means that water is leaking from the tank into the bowl.
Reduced Flush Efficiency: The tank and bowl connection don't maintain water pressure.
Signs of Leaks: Dripping water on the floor, dampness around the base of the tank, or water stains on a finished floor indicate that the rubber gasket has deteriorated or has a broken seal. Note: If it's clean water and odorless, it may be dripping down from the leaky toilet tank. If it's dirty water or smells, it's a wax seal problem from under the toilet base.
Water Damage: Water stains or discoloration near the base of the toilet are signs of floor damage from a toilet leak. It indicate a persistent problem and checking the tank-to-bowl gasket is a relatively quick and easy check.
Uneven Tank Position: If the tank is slightly tilted or uneven, the gasket may be is worn out and no longer providing a proper seal or support.
Rocking or Movement: If the tank moves when you push or wiggle it gently, the gasket is no longer holding the tank securely on the toilet base.

Tools and Materials Needed:

Adjustable wrench
Sponges or towels
Replacement gasket or repair kit (there is minimal differences between brands but the diameter size matters)
Small bucket or large bowl
Putty knife or utility knife (optional)
Screwdriver (optional)
Rubber gloves (optional, this water is clean)

How to Replace a Toilet Gasket

Turn Off the Water Supply: Locate the hose near the toilet base and turn the water supply valve clockwise to stop the water flow.
Drain Toilet Tank

Flush the toilet to drain as much water from the tank as possible.
Remove the tank lid and use a sponge to soak up any excess water.

Disconnect the Water Supply Line

Place a towel on the floor to catch any drips or spills.
Place a bowl or bucket under the water supply line.
Use an adjustable wrench to loosen and disconnect the water supply line from the bottom of the tank. Be prepared for some residual water to spill out.

Remove the Tank from the Bowl

At the bottom of the tank you'll see the toilet bolts that secure the tank to the bowl.
Remove the tank bolt caps. Use an adjustable wrench to loosen and remove the nuts from the bolts. You may need a screwdriver to hold the bolt heads inside the tank while you turn the nuts.
Take note of how the metal and rubber washers are arranged so that you put them back correctly later (rubber against porcelain, metal against the nut).
Close the toilet lid and carefully lift the tank off the bowl (it's heavy) and lay it on a towel or soft surface to prevent damage.

Remove the Old Tank Gasket

The gasket is a large rubber ring on the bottom of the toilet's tank. Common types are black or red.
Pull off the old gasket. If it’s stuck, you can use a utility knife or similar tool to gently pry it loose.

Clean the Area: Clean any hard water residue from the flush valve opening and the bottom of the tank to ensure a good seal for the new gasket.

Install the New Gasket: Place the new gasket over the flush valve opening. It should fit snuggly and might need to be gently stretched to pull it on. Make sure it's evenly pulled on all the way to create a watertight seal.

Reattach the Tank to the Bowl

Carefully lift and lower the tank back onto the bowl, aligning the tank bolt holes in the bowl.
Line up the holes by looking down into the empty tank. Insert the bolts with the rubber washer sitting flush to the porcelain below the metal or plastic washer.
*Remember, the hardware will be in reverse order on the underside of the tank.
Reattach the nuts to the bolts and tighten them evenly. Avoid over-tightening, as this can crack the porcelain. If it's hard to turn the nut, remove it and try again; the last thing you want now is to strip the nut threads. Tighten just enough to create a secure seal.
Replace the bolt covers.

Reconnect the Water Supply Line Hose: Reattach the water supply hose to the bottom of the tank and tighten it securely with an adjustable wrench.

Turn On the Water Supply to Fill the Tank With Water

Turn the water supply line valve counterclockwise to restore the water flow to the toilet.
Allow the tank to fill, and check for any water leakage around the gasket area.

Test the Toilet: Once the tank is full, flush the toilet a few times to ensure that you have a tight seal.

Other Reasons the Toilet May be Running

Flapper Assembly: A rubber seal is at the toilet tank's base attached to the flush valve. Without a strong seal at the flapper valve connection, gallons of water will constantly trickle into the bowl and be replenished in the tank.
Fill Valve: Found on the tank's left side, this valve controls water level. If set too low, the flush will be weak. Set too high and water will constantly flow into the overflow tube.
Float: Typically a ball or cup, it regulates water level. Damage can lead to tank overflow and continuous water replenishment.
Flush Handle: A broken or stuck handle keeps the flush mechanism engaged, resulting in continuous water flow.

This article first appeared on Men's Journal and was syndicated with permission.

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