A toilet that refills every few minutes usually isn't broken its flapper just quit sealing. This 3-inch rubber flapper (MPN: G0099788) closes off the flush valve opening in Gerber high-efficiency toilets rated at 1.28 gallons per flush. Made from chlorine-resistant rubber and finished in blue, it drops into 3-inch flush valve openings without cutting, gluing, or special tools, restoring a tight seal so the tank stops running and each flush uses exactly the water it's designed to use. Plumbing Supply And More stocks this flapper because it's one of the most frequently requested toilet parts for Gerber's high-efficiency lineup, and because the difference between this part and its look-alike sibling trips up a lot of DIY buyers. Many of the toilets this flapper services carry a WaterSense label from the fixture manufacturer, meaning the bowl, tank, and flush valve were tested together as a complete high-efficiency toilet (HET) assembly at the 1.28 gpf rating. The flapper itself isn't separately certified — it's a wear component — but keeping it matched to the original valve size and rubber spec is what lets the whole assembly keep performing at that rated flow instead of drifting upward as the seal ages. What Makes This 3-Inch Rubber Flapper Different From the 99-770 This flapper is solid on the underside — no secondary hole. That single detail separates it from Gerber's 99-770 flapper, which does have an extra hole molded into the bottom face and is built for older 1.6-gallon tank models. Buyers who order the wrong one typically get a toilet that either doesn't flush completely or flushes twice as much water as intended. Across the top rim, this flapper measures approximately 3-5/8 inches, matching the seat diameter of a 3-inch flush valve without gaps at the edges. It's molded, not stamped, so the sealing lip keeps its shape instead of curling after repeated flushing cycles. Toilet Parts Compatibility Snapshot: Fits 3-inch flush valve seats only & not usable on 2-inch valve openings Replaces the earlier Gerber G0099833 flapper directly Distinct from the 99-770 (extra underside hole, 1.6 gpf tanks) Ships with a stainless steel lift chain and clip hook attached Soft Rubber Versus Rigid Flapper Designs in Gerber's Product Line Gerber lists two general flapper styles across its toilet parts catalog: a soft, fully flexible rubber disc — the type this part represents — and a rigid flapper with a stiffer backing plate used in some later-production tank models. Soft flappers like this one flex more readily off the valve seat when the lift chain pulls, which tends to produce a slightly faster full-open action on the first second of the flush cycle. The trade-off runs the other direction over time: a rigid backing resists warping longer under sustained tank pressure, while a soft flapper depends more heavily on rubber quality to avoid curling at the edges after repeated cycles. Choosing the chlorine-resistant compound used in this flapper offsets that trade-off, since edge curling is almost always a chemical breakdown issue rather than a mechanical one. Rubber Construction Built for Repeated Tank Chemical Exposure Toilet tank water isn't always plain water — bowl tablets, hard-water minerals, and cleaning drop-ins all sit against the flapper seal around the clock. The rubber compound used in this part is formulated to resist chlorine breakdown, which is the single most common reason inexpensive flappers go soft, swell, or crack within a year of installation. A softened or swollen flapper won't seat flush against the valve opening, and that's the mechanical root of most "phantom flushing" tanks — the quiet refill cycle that runs every ten to twenty minutes even when nobody has touched the handle. Because this flapper holds its density longer, the tank-to-bowl seal stays tight through years of tablet or drop-in cleaner exposure rather than months. How Does This Flapper's Seal Control Water Use in a 1.28 GPF Toilet? The blue rubber disc rests directly over the flush valve seat, held shut by tank water pressure until the flush lever lifts it via the attached chain. Once lifted, it stays open long enough for the full 1.28-gallon charge to clear the bowl,
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