Open the doors to the cabinet under your sink. Reach inside and gently hit the interior side of the flat panels above the cabinet doors until the panel falls out of the cabinet.
Lay the flat panel down on the countertop. Mark the short edges of the panel into thirds. Choose and label the top of the panel for future identification.
Attach a 2-inch vinyl tilt hinge, which looks like a sliding bar inside of a hinge, to the flat panel. Use the screws found in the hinge package and a cordless drill with a Phillips head bit to attach the hinges to each side end of the flat panel, flush with the edge at the line that shows the bottom third of the panel.
Attach two 1-inch metal hinges to the bottom, long edge of the flat panel 1 inch from each corner, using the screws found in the hinge package and a cordless drill with a Phillips head bit.
Measure 1/2 inch up from the bottom and 1 inch in from each side of the flat panel. Attach two plastic 2-by-1-inch sponge trays to the flat panel using screws and the cordless drill. Attach the plastic sponge trays with the open ends facing up.
Attach the four hinges on the flat panel to the inside of the sink cabinet using screws and the cordless drill. You may need to lean inside the cabinet to reach the hinges properly.