To use a hydro-vacuum, push the attachment into the gravel and suck on the other end of the hose to get the water started. Make sure you hold the outer end of the hose lower than the rim of the tank. As soon as you see the water in the hose cross over the top of the tank, place the end of the hose in a bucket positioned below the water level.
You will see the gravel swirl around in the large end of the hydro-vacuum, releasing clouds of waste material that will be drawn out of the tank along with the siphoned water. By pulling the attachment out of the gravel and pushing it into the gravel nearby, you will be able to effectively clean the gravel bed without removing the gravel from the tank.
Feeling that this activity will disturb the nitrifying bacteria in the gravel, some hobbyists vacuum only half of the gravel bed with each water change, alternating from one side to the other each time. Cleaning the gravel really shouldn't have any ill effects on the bacteria, though, so this caution is probably not necessary.
Every two to eight weeks, depending on how the tank is managed and what sort of fish it houses, the filter materials in the power filter will need to be changed. If the mechanical filter material is reusable, place it in a bucket with some aquarium water and squeeze it a few times to clean it or simply rinse it with tap water.
If you use tap water, make sure it is the same temperature as the tank water. If you are using some type of bio-media in the power filter, follow the same procedure as for the mechanical filter material.
The granular activated carbon will have to be replaced. Once the carbon is saturated with molecules it can't absorb any more.
Some hobbyists test the carbon by tinting the water very lightly with a harmless food dye. If the dye is removed by the carbon, it does not need to be replaced. It is easier to simply use new carbon when cleaning or changing the mechanical filter material.
This is all the maintenance an aquarium should require. Do not tear the tank down, clean everything thoroughly, and then set it up again. This only destroys all of the beneficial bacteria in the aquarium, forcing you to break in the tank again. If an aquarium requires that kind of cleaning, there are severe overcrowding or maintenance problems that need to be dealt with.