I have about four Top Fin Gravel Vacuums in various sizes for my fish aquariums. These vacuums are great for when I do a water change on a tank.
The vacuum is made up of a larger sized tube attached to a long thinner tube that you use to siphon the water out of your tank so that you can put fresh water back in. I empty the old water into a five gallon water jug and I put a combination of RO and well water back into the tank that I am doing a water change on.
The larger tube of the vacuum gets put into the tank, the smaller tube goes into the jug so that the water drains into it. There is a knack to getting the vacuum action started, but once you know how to do it, it is relatively easy to siphon out old water to enable you to put in fresh. I also use the siphon as a vacuum. Putting the larger tube into the gravel will vacuum up the dirt, debris, old food waste, etc. without taking the gravel. That way, you are actually vacuuming the dirt out of your tank and leaving a cleaner tank behind.
These vacuums work great. I have had them for years and I think I only had to replace one because it cracked. They are relatively inexpensive and easy to use. They make water changes easier to do, and anything that makes tank maintenance more easy is OK by me.