Greetings,
I purchased a gravel vacuum for about $4.00 at the local pet store. I don't have gravel, but was hoping to just use it to clean up the tank in between changes.
If you have a tank full of water, it should work OK. If you have just a half a tank (3"-6" of water) it's a pain. There's not enough water to get the vacuum working.
They're very basic. You start the hose by forcing water into the tube and it suctions the water into an empty bucket. It does pick up stuff - water, waste, food, and UFOs (unidentified floating objects). Once your done, refill the tank with water.
-Ravon