Im pretty new at having a fish tank and I'm only 15 so i'm always thinking of bizarre ideas and i was thinking would it be possible to hook up a basic gravel vac to a HOB filter or a cansiter filter? I have a HOB filter on my 20 gallon tank and i wanna keep vaccuming my gravel but by the time im 1/4 the way through half my water is gone. would this at all be possible?

thanks JOMA

__________________
"just do it"

You need to figure out how much water you are taking out in how much time, this is done by taking a gallon bucket and filling it up to the mark, time how long it takes to do this.

Then you simply buy a powerhead that will pump as much water back as you are putting in. Remember that if a powerhead pumps 300GPH at 0level then at 1ft it will pump less. The powerhead box should have a diagram of this

im not a expert but i think it would over load your filtration with all the poop that is built up in the gravel best bet is to get water from fish store with 5gl buckets and when it gets low refill it but make sure first your water matches the stores and iv never had a problem with cleaning my tanks 55gl with 5 plecos and 7 parrot fish oh boy did i have to clean gravel make sure the heater doesn't get dry wile still plugged in it will explode,. once i brought the water down as far as the fish can fit just to save my self from lifting buckets

you're fine, you wont clean it at one sitting.
I do 50%'s on my smaller tanks and less on my bigger tanks.

Example- 10g snail/feeder fish tank. Before I got my turtle it was snails and never cleaned it(2 AC20's on it) well put the feeders in and moved soem decor, the water went jet black. im still doing PWC's to clean it up but its been 2 weeks of PWC's to get it close to being perfect.
the gravel must not be spotless, if so bacteria will go bye bye thus causing other issues in the tank. do a little bit at a time and it will get clean.