Or rather, getting them to clean themselves.

Mix up a salt brine, and give them an hour to pump the clean water through themselves to purge gunk and sand.

• One Liter of water (about 4 cups)
• 30 grams of kosher salt or sea salt (about 2 tablespoons)

Mix salt and water, making sure its all disolved. Pour brine over the clams. Wait at least an hour, maybe more.