According to Outer Banks, cleaning coins found on the beach is an easy job. First of all he doesn't clean pennies as he doesn't think its worth the time. First use a rock tumbler. They're not expensive and cost under $100.00. Toss the coins in a tumbler with small rocks or gravel as this helps clean and separate the coins. Use a couple of squirts of dishwashing liquid and water about 3/4 full. Let it tumble about three to four hours. Using a colander rinse your coins once tumbling is completed. Let your coins dry on newspaper and your job is complete.