You don't. I place about five cups of sand in a bucket, and rinse it (under the tap, or outside with the hose) five times. It gets the worst of the dirt. Then add the sand to the empty (no water) tank, and do the next bucket. When you're finished, arrange the hardscape materials. You can then fill the tank; if you have plants to plant, half fill the tank, plant them, then drain the water down to the sand. use a bowl to run/pour the fresh water into as this will avoid stirring up too much. Add dechlorinator. Done. It will settle out, more likely you'll have a bacterial bloom if hazy, that will clear on its own.