We take clams off our beach on Hood Canal regularly. Bring them back in 5 gallon buckets, or cooler with salt water. We never bother with adding anything to the water to get them to purge. Never had a problem with sand. One thing I do to get several days, if not a week out of them, is to take some of the salt water out and freeze it. Big blocks that last several hours. Keep rotating in fresh ice. They stay real happy. Works the same just putting them in the fridge, but there isn't always room. As far as cooking them, we don't cook them in water. Just throw them in a pan, add anything you want for flavor, be it shallots, garlic, splash of white wine. They have plenty of liquid in them. Cook until all are open. Melted butter with a touch of cayenne pepper for heat.