Step 2 · Remove the Disposal Knockout Plug
Locate the horizontal inlet nipple on the upper side of the garbage disposal body; this is where the dishwasher hose will connect. If a dishwasher has never been connected, this inlet is sealed by a 'knockout plug'. Insert the tip of a flathead screwdriver into the inlet nipple until it rests against the plug. Firmly tap the end of the screwdriver handle with a hammer to dislodge the plug, which will fall into the disposal's grinding chamber. Reach into the disposal from the sink drain above and retrieve the plastic plug. If you cannot grab it with your fingers, use needle-nose pliers.