The Miracle-Gro Feeder operates with a simple venturi action, were the water passing through the head under pressure, draws up small quantities of the concentrated feed solution from the container. A fine jet of water constantly squirts water into the container to agitate and dissolve the Miracle-Gro Food to form a dark blue concentrated solution. When the solution becomes a paler blue, this shows that the feed is running out and needs to be replaced. To empty the container of water, with the water passing through the head, turn it upside down, the water will drain out of it. Once empty, remove and fill with up to a maximum of 500grams, one sachet of Miracle-Gro Soluble Plant Food.