They are all by gravity. Called gravel vacs. You fill the whole canister with water by laying it on it's side in the tank, put the other end in a bucket that is lower than the tank. When the canister is filled, aim it toward the sand and pump it up and down a couple times to get the water flowing. You should just be able to push the end of the canister into the sand then lift it up and it should suck up all the "junk" but let the sand fall back out. And it will keep sucking water and debris out until you life the entire thing out of the water. The first time I tried it, it took me FOREVER to get it going! But now I can do it on the first try. Good luck!