What you need:
Pool Filter Sand
5 Gallon Bucket
Water Hose with Jet Spray nozel on the end.
Poor about 1.5 gallons worth of sand in. (See Picture)
Fill the bucket with water from the hose.. Be sure to heavily stir the sand up in the bucket as you spray the water in.
Now tip the bucket and let all of the dirty water out. Stop when sand starts to poor out. Do not let the water settle after you feel the bucket.
Keep repeating this until the water is clear! It will take a minimum of 10 times.
When you are done this is what the water should look like:
You have now removed the things that will cloud up your water from the filter sand. The amount cleaned is enough to do a 15 gallon tank.
Here's the tank 1 day after sand was added.