spud washer
A flanged rubber or foam ring that covers the spud nut on the flush mechanism of a toilet, cushioning the tank-bowl juncture to prevent leaks.
spud washer: rubber seal that stops your toilet tank leaking
A spud washer is a flanged ring, typically made from rubber or closed-cell foam, that sits under the spud nut where a toilet tank bolts to the bowl. The spud nut itself is a large hex nut that compresses the flush valve (spud) against the tank outlet, creating a watertight seal. The washer cushions that joint and prevents water from weeping out between the tank and bowl during normal operation and under the weight of a full tank.
The washer is positioned on the threaded tailpiece of the flush valve, below the tank, before the spud nut is threaded on and tightened. Most spud washers are between 1.5 and 2 inches in diameter, with a tapered or beveled edge that helps them seat properly against the curved underside of the tank outlet. Rubber versions are more common in residential work because they remain flexible over decades; foam washers are cheaper but compress over time and may need replacement during a tank-bowl reseal.
Failure and replacement
A failed spud washer shows itself as water dripping or running from under the tank onto the floor or inside the bowl. The washer hardens and flattens with age, especially if the spud nut was over-tightened or if mineral deposits built up in hard water areas. When a tank-to-bowl leak appears, the spud washer is often the culprit, and replacing it requires draining the tank, unbolting it from the bowl, removing the old nut and washer, and installing a new washer before reassembly. A new washer costs only a few dollars but is often overlooked in favor of replacing the entire tank.
The term spud comes from the flush valve assembly itself (the main moving part inside the tank), so the spud nut secures the spud, and the spud washer supports it. In older systems, plumbers sometimes layered multiple thin rubber or cork washers to achieve the right compression; modern single-piece washers eliminate that guesswork. Aftermarket foam or wax-impregnated varieties exist for specific applications, but standard rubber spud washers work for the vast majority of two-piece tank-and-bowl toilets.