You clean the sand by holding the gravel vaccum slightly above the sand as opposed to shoving it down into the sand. All of the waste ,debri,etc should remain on the surface of the sand making shoving the gravel vac into it unneccessary. After you clean the sand in this way, you simply sift through the sand with your fingers or plastic fork or other tool to keep pockets of gas from building up. I have found that if sand is kept at no more than two inches deep,, then there is little chance of said gas pockets forming. the use of trumpet snails can also be utilized thus making the sifting unneccessary.
You clean gravel before using in the aquarium by rinsing it several times in a tub or bucket or by using a collander(not sure of spelling).
Sand will need to be rinsed ,rinsed,rinsed,and rinsed again to help keep it from clouding and to remove very fine grains and or dirt that may be found in it. Approx, one pound of sand for each gal for approx inch and a half of depth in the aquarium.