Fluidmaster���s 400AW504 offers a fast and effective solution for fixing problem toilets. This toilet repair kit quickly fixes noise and running toilet issues. Including the 400A toilet fill valve, a universal and code approved anti-siphon design, that won't contaminate the fresh water supply. Also, featuring the flexible 504 flapper for 2 in. flush valve toilets. Best for toilets 3.5 GPF pre-1994. The toilet fill valve upgrades your fill with quiet power, while the flapper fit's most models and is chlorine resistant.