How to Replace a Screw Top on a Garbage Disposal

Tighten an adjustable wrench around the nut that connects the P-trap -- the U-shaped pipe -- to the garbage disposal's intake pipe. Crank the wrench to loosen the nut and slide the P-trap off the intake pipe.

Hold a flat-head screwdriver against the old assembly's mounting lug -- the metal ring attached to the mounting assembly's side -- and place one hand underneath the garbage disposal. Use the screwdriver to push the mounting lug all the way to the left. Remove the disposal from the mounting assembly and set it down.

Reach underneath the sink with a flat-head screwdriver and loosen the three screws that hold the mounting assembly in place. Pull the snap ring off the assembly's bottom and pull the entire assembly down. Push the sink flange up and out of the sink's drain hole.

Roll plumber's putty into a 3/4-inch thick rope and wrap it around the new sink flange's bottom lip. Firmly push the sink flange into the sink's drain hole.

Ask a friend to hold the sink flange in place while you slide the fiber gasket, triangular back-up ring and mounting ring onto its bottom. Stretch the snap ring around the mounting ring's groove. Use a flat-head screwdriver to tighten the three screws to hold everything in place.

Remove the excess plumber's putty that oozed out from underneath the sink flange, with a putty knife.

Lift the disposer up to the mounting assembly. Insert the disposer's tabs into the assembly's gaps. Hold a screwdriver against the new assembly's mounting lug and push it to the left.