Harv...
Fillmaster and early model fluidmaster fill valves had the actual valve mechanism at the base of the valve which was under the standing water level in the tank.
In order to insure there can be no possibility of cross contamination between the standing water in the tank and the house potable water supply the codes now require the actual fill valve discharge port to be a minimum of 1" above the top of the tank standpipe. (International Residential Code 3105.1 & Uniform Plumbing Code T 10.1)
Most of the universal replacement fill valves such as Fluidmasters have a telescoping section that can be extended to raise the fill valve above the water line. This is a very important step that is often overlooked when installing replacement valves.
