A method of using a backflow box with a water-using appliance comprising providing a backflow box including a backflow preventer and drainage; installing the backflow box in a wall cavity of a building in an accessible and viewable location; coupling the backflow preventer of the backflow box to a water supply and the water-using appliance; coupling the drainage of the backflow box to drain line of the building; inhibiting backflow from the water-using appliance from flowing into the water supply backflow preventer; and draining backflow through the drainage of the backflow box to the drain line of the building.