Seeing as its already in your tank with no fish, stir it up, water change (75%) - repeat several times in a row if possible across a few days, filter running with fine sponge/wool (which you will later throw out). You're basically just washing the sand in the tank doing this, which is all you can do really. Whilst it will take about the same time in days to clear if you just did a single 50% change a day, doing this initially will mean that if the sand is disturbed by you or your fish, it will not instantly cloud the tank.