Summarize:

Place about 1 Tablespoon (14.7 ml) of dish soap into a shallow pan about with 1 quart (946 ml) of hot water. Be aware that the ink from the erasers may stain the pan. Place the erasers into the pan of hot water and leave them to soak for 20 minutes (or more). Then rinse them under running water until all ink is removed and the water runs clear. In order for you to be able to use the dry erasers, they must be completely dry. The best way to effectively dry them out after washing is to set them in direct sunlight for 1-2 hours.
Fill a pan with soapy water. Soak the erasers. Set the erasers in the sun.