Aquarium Vacuums are a simple and easy way to help maintain a clean aquarium. The wide part of the tube should be almost, but not quite as tall as your tank is, as this will make operation of the gravel vac much easier. The narrower siphon tube will need to be 4-6' long to make it easy for you to reach the bucket and move the gravel vacuum around as necessary. Gravel vacuums are used when performing your regular weekly 10-15% water change to clean part of the gravel while removing the water. This is important in all aquariums.