A sand and sea diffuser typically refers to a type of essential oil diffuser that is designed to create a relaxing, beachy atmosphere in your home or office. To use a sand and sea diffuser, you would typically fill the water tank with water and a few drops of your favorite essential oil, and then turn the diffuser on. As the diffuser releases the scented mist into the air, it can help to create a calming and rejuvenating environment.