i put my sand into an old pillow case and sloshed it under the tap for 10 minutes. this is a good way to get rid of the ultra-fine particles that would cause clouding in your tank
I also used the bucket method.....half a bucklet of sand, rest filled with water, and stir it around and empty out the dirty water......then repeat until you don't get much dirt coming out (mine was about three times as well). Seems to take forever in a large tank, but well worth the effort!!
same as what everyone else has said I suppose - put some sand in a clean bucket and run water into it. Mix the sand slightly and keep putting in & pouring out the water until it looks clear.