A new kitchen sink and a disposal change how the whole drain works, so it pays to plan both together. The sink sets the drain location. The disposal hangs from the sink flange and adds a second outlet for the trap. The dishwasher drain connects to the disposal, and the faucet needs supply lines. Mistakes in any one of those show up as leaks or backups later.
This guide covers a drop-in sink and a standard continuous-feed disposal. If the disposal is the only change, our garbage disposal page covers repair and replacement. For a larger kitchen remodel with new supply lines, see plumbing installation.
Preparation.
Before you start: plan and gather.
- Measure the cutout in the counter and the sink you have chosen. A drop-in sink needs a cutout slightly smaller than the rim.
- Check the cabinet base for room. A disposal hangs about eight to twelve inches below the sink, and a deep sink plus a large disposal can crowd the trap.
- Confirm the electrical. A disposal needs a switched outlet under the sink or a hardwired connection, and a hardwired one may need a permit and a licensed electrician.
- Gather plumber's putty, a disposal kit with mounting assembly, a new trap kit, a basin wrench and silicone sealant.
Sink steps.
Installing the sink.
Shut off water and power.
Close the shutoffs under the sink and switch off the disposal circuit. Disconnect the old faucet supply lines, the trap and the old drain.
.Lift out the old sink.
Cut the caulk seal around the rim, and push the sink up from below. Clean the counter edge.
.Set the strainer and faucet first.
Fit the strainer basket with putty or a gasket, and install the faucet on the new sink before it goes in the counter. It is far easier on a bench than under the cabinet.
.Drop in the sink.
Run a bead of silicone around the rim, lower the sink and secure it with the clips from below.
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Disposal steps.
Mounting the disposal.
Remove the dishwasher knockout plug.
If a dishwasher will connect, knock out the plug inside the disposal's dishwasher inlet with a screwdriver and hammer, and remove the plug. Forgetting this step blocks the dishwasher drain entirely.
.Attach the mounting assembly.
Seat the sink flange in putty, fit the gasket, backup ring and snap ring, and tighten the mounting screws evenly.
.Hang the disposal.
Lift it onto the mounting ring and rotate until the lugs lock. Align the outlet with the trap.
.Connect the drain and the dishwasher hose.
Attach the discharge elbow with its gasket. Clamp the dishwasher hose to the inlet, with a high loop or an air gap.
.Connect power.
Plug it in, or wire it to the junction box with the power off, following the instructions.
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Test for leaks.
Fill the sink with water, release it and watch every joint. Run the disposal with cold water and check again. Dry paper towels held under each joint show a seep that your eye might miss.
Troubleshooting.
Common mistakes.
| Mistake | What happens | Fix |
|---|---|---|
| Dishwasher knockout left in. | Dishwasher will not drain. | Remove the plug from the inlet. |
| Mounting ring not seated evenly. | Leak at the sink flange. | Loosen, reseat putty and retighten evenly. |
| Trap misaligned. | Slow drain or leak at the slip nut. | Realign and use new washers. |
| No high loop on the dishwasher hose. | Dirty water can flow back into the dishwasher. | Raise the hose or add an air gap. |
Permits and older Salem kitchens.
Salem requires permits for plumbing work, and applications are filed online through the city's Inspectional Services system, with the permit office reachable at 978-619-5641. Replacing a sink and a disposal in the same place is a routine repair. Moving the sink, adding a drain or hardwiring a disposal may involve plumbing and electrical permits, so ask before you start.
Many older Salem kitchens have drain pipe in cast iron or galvanized steel behind the wall, and the first sign of trouble after a new install is often a slow drain that was already partly blocked. If the drain is slow before you connect the new unit, have the line looked at with drain cleaning first.
If you would rather hand off the hookup, we dispatch to Salem and to Beverly, and can do the supply, drain and disposal connections while you handle the counter.
Questions.
Sink and disposal installation questions from Salem homeowners.
Many homeowners can, if they take their time and the wiring is a plug-in unit. Hardwired connections should be done by someone qualified.
Local code decides. A high loop is common, and some areas require an air gap. Ask Salem Inspectional Services or your plumber.
A half to three quarter horsepower unit suits most homes. Larger households or heavy use may justify more.
A misaligned trap, a partly blocked line or a mounting issue. Check the trap first.
A disposal pushes scraps into the line, which is harder on scaled cast iron. If your pipes are old, use it lightly and consider a camera check.