The Self-Start Siphon feature has made aquarium maintenance a whole lot easier. With the Gravel Vacuum Cleaner completely submerged in the water simply move it up and down a few times to activate the Self-Start Siphon. Gravel Vacuum Cleaners are designed to separate and remove debris from the aquarium during routine water changes. The Medium Gravel Vacuum Cleaner features a 2” diameter x 10” long cylinder with a 56” long hose. It is ideal for use in tanks with up to a 55 gallon capacity. The Wide-Mouth Nozzle increases your surface coverage by about 20% allowing you to clean more gravel surface without draining too much water.