chuck it all in a bucket, then in the bath blast it with cold water, then turn the tap off and leave for a few seconds so the big sand stays at the bottom then pour out water but stop just before the sand comes out, and repeat and repeat and repeat again and eventually you'll get to the point where as you blast it with cold water you will see the big sand particles immediately drop to the bottom of the bucket and the water will be pretty dam clear! dont forget to swirl it round with your hand every now and again, but might be worth using some hot water too as your hand goes freeeeezinnngg!
best of luck