When I lived in Maine we would sometimes eat steamed mussels and steamer clams. To purge the sand I would keep them live in the fridge in salted water and feed them sprinkles of corn muffin mix for a couple of days. The critters would expell the sand and fill their tummies with sweet muffin mix. Yum.
As a midwesterner I can advise that the same technique does not work for "prairie oysters".