FillMAGIC™ 2 Pack Water Saving Toilet Tank Overflow Fill Cycle Diverter Valve saves 0.5 to 1.5 gallons of water per flush. The toilet tank and bowl fill at the same time, but they dont fill at the same rate — the bowl fills faster. Because the fill valve doesnt shut off until the tank is full, water continues to be fed to the bowl. So, where does this extra water go? Straight down the drain! The FillMAGIC™ Diverter Valve fills the toilet tank faster and reduces water loss through the bowl by dividing the flow between the overflow tube and directing a portion of the flow into the toilet tank itself. Install easily without tools.