This gravel vacuum is ideal for changing the water in small to medium sized aquariums. It has an easy start hand pump to get the siphon started. Simply put one end in the tank and the other in a bucket. Squeeze the bulb a few times and the water will start flowing. It can also be used for refilling the aquarium if you place the bucket of fresh water above the tank. With the included attachments, it can also be used to vacuum the gravel. The highly flexible tube makes it easy to get into all corners and around decor. There is a removable strainer in the nozzle to prevent fish from being sucked up.