Place the end of a garden hose in the bottom of a 5 gallon bucket.
Fill bucket 3/4 full with sand.
Turn water on to a slow-moderate speed. You want to agitate the sand, but not blow it out of the bucket.
Slowly move the end of the hose up and down and around the bottom of the bucket.
As the water flows out and the sand is agitated, all the smaller, lighter particles will be carried out with the water. The larger heavier particles will stay in the bucket.
After about 15 minutes or so, the water coming from the bucket should be clear. At this point, dump the sand into the tank, and start with the next batch, repeating the above steps.