If you already have a garbage disposal, replacing it should take less than an hour, as long as the new one is the same size and has its outlet in the same position. (If you upgrade to a larger disposal you will probably need to cut a trap pipe or two to make it fit.) If you will put in a new disposal where there was none before, you will need to assemble a new trap along with the disposal.
You will also need an electrical receptacle that is controlled by a wall switch, which you will plug the disposal into. If you don’t have one, hire an electrician to install one, or consult a book such as Wiring Complete (The Taunton Press, 2017).
A 1⁄3-horsepower disposal does well for light duty; a 1⁄2-horsepower unit suits most household needs. If you often want to grind things like lemon rinds, it’s a good idea to install one that pulls 3⁄4 or even 1 horsepower.
KNOCK OUT THE DRAIN HOLE FOR THE DISHWASHER. If you plan to run the dishwasher drain line through the disposal (which may or may not be up to code in your area), open the drain hole by tapping the knockout slug with a hammer and screwdriver. Be sure to remove the slug from the inside of the disposal.
ATTACH THE ELBOW. Some trap setups call for an elbow coming out of the disposal. The elbow is usually provided along with the disposal. To install one, slip a rubber washer into the opening, set the elbow in place, and slide the mounting washer into place. Drive two bolts to attach the mounting washer, as shown.
TIP: If you are replacing a disposal with one of the same size, you can probably reuse the mounting bracket (the part that fits in the sink’s hole), which will spare you the most difficult part of the job.
1. REMOVE THE OLD BASKET STRAINER. To remove the old basket-strainer mounting bracket, work from below and use a spud wrench to unscrew the mounting nut.Or tap with the claws of a hammer or with a hammer and screwdriver.Once the nut is off, pull the strainer out from above.
2. DISASSEMBLE THE MOUNTING RING. To disassemble the mounting bracket, loosen the three screws
Use a small slot screwdriver or two to pry off the ring.
3. PROVIDE POWER. There should be a switched source of power. Test that it turns on with a switch. Before proceeding with the next steps, shut off power and test to verify that power is off.
4. INSTALL THE CLAMP CONNECTOR. Loosen the screw that holds the electrical access cover and remove the cover. Pull the black and white wires out.Remove the nut from a clamp connector.
Insert the connector’s threads into the hole in the disposal, and thread the nut back on from inside the disposal. It’s usually easiest to hold the nut still while you turn the connector. Tighten the connector with pliers, but leave the clamping screws loose.
TIP: The cable shown here is metallic sheathed, but yours may be plastic sheathed. The type of cable clamp shown here works for both types of cable.
5. MAKE THE ELECTRICAL CONNECTIONS. Strip 3⁄4 in. to 1 in. of insulation from all the wires. Poke the cable into the disposal’s hole and pull its wires through the access opening. Tighten a 3⁄8-in. cable clamp to hold the cable securely (top).Use wire nuts to make firm electrical connections: black wire to black wire (or colored wire, in this case orange) and white wire to white wire. There should be no visible bare wire; wrap the connections with electrician’s tape to be sure.If there is a third wire, green or bare, connect it to the green grounding screw. Push the wires back into the disposal, and replace the cover.
6. PRESS THE FLANGE WITH PUTTY. Roll out a rope of plumber’s putty with your hands, place it on the underside of the bracket’s flange, and press it all around to seal tight.Press the flange into the sink’s hole. Have a helper hold the flange in place as you perform the next step.
7. ASSEMBLE THE BRACKET. Working from below, slip on the cardboard washer, then the triangular washer, then the bracket with the screws. Now comes the first tricky part: Hold the ring in position, then use a screwdriver or two to slip the ring onto the groove in the bracket’s body. This may take several attempts, but be patient and you’ll get it.
8. TIGHTEN THE THREE SCREWS. Tighten the three screws, alternating so they all end up about the same length. That will ensure that the disposal hangs straight down. Have your helper check that the flange is centered on the sink’s hole. If not, loosen the screws, center it, and retighten.
TIP: Unscrew the three mounting screws nearly all the way; that will make it easier to mount the bracket.
9. MOUNT THE DISPOSAL. And now, the second tricky part: Holding the disposal straight vertically, push it up onto the mounting bracket. When you feel it slide up a bit, turn the locking ring by hand to get it started. Then use a screwdriver to finish turning the locking nut. If you don’t succeed the first time, get yourself into a comfortable position and try again, taking care to keep the disposal plumb. Assemble the trap and perhaps the dishwasher hose, and test.
Excerpted from Plumbing (The Taunton Press, 2016) by Steve Cory.
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