Install the garbage disposal first, then connect the dishwasher to it
A garbage disposal and dishwasher work best when installed as a pair: the dishwasher drains into the disposal, which grinds food waste and sends it down the drain line. You install the disposal under the sink first, then run the dishwasher's drain hose to the disposal's inlet port. Both jobs require basic plumbing knowledge, hand tools, and about two to four hours total. If your sink currently has no disposal, you will need to remove the existing strainer basket and knockout plug. If you are replacing an old disposal, the work is faster because the mounting hardware is already in place.
This guide covers the standard setup for a single-bowl or double-bowl sink with a new or replacement disposal. The process differs slightly if you are adding a dishwasher to an existing disposal, or if your sink has a garbage disposal on one side and a regular drain on the other. Read through the full installation steps before you begin, because some steps must happen in a specific order and mistakes can mean water leaks or a disposal that does not turn on.
Key Takeaways
- Turn off the power at the breaker and the water supply before you start any work under the sink.
- Remove the old strainer basket and mounting ring, then install the new disposal's sink flange and mounting assembly before you connect any drain lines.
- The dishwasher drain hose connects to the disposal's inlet port, which is usually a threaded opening on the side of the unit.
- Test the disposal and dishwasher separately before you run them together, because leaks are easier to spot and fix before the cabinet is closed.
- If your disposal has no inlet port, you will need a dishwasher adapter kit, which costs between fifteen and thirty dollars.
What you need before you start
Gather your tools and materials in one place so you do not have to stop mid-job. For the disposal, you will need an adjustable wrench, a screwdriver (usually Phillips head), a putty knife, plumber's putty, and a bucket to catch water. For the dishwasher connection, you need the dishwasher drain hose (usually included with the dishwasher or disposal kit), a hose clamp, and possibly a dishwasher adapter kit if your disposal does not have an inlet port.
Check your disposal's manual to see whether it has a side inlet port for the dishwasher drain. Most modern disposals do; older models and some budget models do not. If yours does not have one, a dishwasher adapter kit lets you drill or punch a hole in the disposal's side and install a threaded port. The kit usually includes the port, a rubber gasket, and a locknut. You will also need a drill with a metal bit, or a punch tool if the kit includes one.
Before you buy anything, confirm that your sink has a garbage disposal outlet. If your sink drains to a septic system rather than a municipal sewer, check your septic system's manual or call your septic service — some systems do not handle ground food waste well. If you are unsure, ask your plumber or local health department.
Turn off power and water, then remove the old strainer
Go to your electrical panel and switch off the breaker that controls the kitchen outlets. Test the outlet with a lamp or phone charger to confirm the power is off. Then turn off the water supply under the sink by closing the shut-off valve on both the hot and cold lines. If you do not have shut-off valves under the sink, close the main water shut-off for your house.
Place a bucket under the sink to catch water from the drain line. Use a wrench to loosen the slip nuts (the large nuts that hold the drain pipes together) and remove the P-trap — the U-shaped pipe under the sink. Set it aside in the bucket. If your sink has a garbage disposal already, unplug it or switch off its breaker, then loosen the mounting bolts that hold it to the sink and remove it. Save the mounting ring if it is in good condition.
If you are starting with a regular sink strainer, use a wrench to loosen the large locknut under the sink that holds the strainer basket in place. From above the sink, push the old strainer basket up and out. Scrape away the old putty with a putty knife. Wipe the sink opening clean with a damp cloth and let it dry completely.
Install the disposal's sink flange and mounting assembly
The sink flange is the ring that sits on top of the sink opening. Roll a rope of plumber's putty about the thickness of a pencil and press it around the underside of the new flange. Push the flange down into the sink opening from above, pressing it firmly so the putty seals the gap. From underneath the sink, slide the rubber gasket, then the metal mounting ring, then the locknut onto the threaded part of the flange. Hand-tighten the locknut first, then use a wrench to tighten it another quarter turn — do not over-tighten, because you can crack the sink.
Wipe away any putty that squeezed out around the flange with a damp cloth. Let the putty cure for the time listed on the package, usually 24 hours, before you run water. While the putty cures, you can prepare the disposal unit and dishwasher hose, but do not install the disposal onto the mounting ring yet.
Prepare the disposal and connect the dishwasher drain hose
Before you mount the disposal, check whether it has a side inlet port for the dishwasher drain. Look at the side of the disposal unit for a threaded opening or a knockout plug (a small plastic or metal disc). If you see a knockout plug, use a screwdriver to pry it out or a drill to punch through it. If your disposal has neither, you will need to install a dishwasher adapter kit following the kit's instructions.
If the disposal has a threaded inlet port, the dishwasher drain hose will screw into it later. If it has a knockout plug, remove it now. Some disposals come with a dishwasher port already installed; if yours does, you can skip this step.
Do not connect the dishwasher drain hose to the disposal yet. You will do that after the disposal is mounted and the putty has cured. For now, just confirm that the hose reaches from the dishwasher to the disposal location without kinks or sharp bends.
Mount the disposal and reconnect the drain lines
Once the putty has cured, lift the disposal up to the mounting ring under the sink. The disposal has three or four mounting tabs that fit into slots on the mounting ring. Align the tabs with the slots and rotate the disposal clockwise until it locks in place. You should hear or feel a click. Do not force it; if it does not lock smoothly, remove it and check that the tabs are aligned with the slots.
Now reconnect the drain line. If your sink has two bowls and only one has a disposal, the other bowl's drain line connects to a tee fitting, which then connects to the disposal's outlet. If both bowls drain to the same disposal, use a tee fitting to combine them. Slide the slip nuts back onto the drain pipes and hand-tighten them, then use a wrench to tighten them another quarter turn. Do not over-tighten, because you can crack the plastic fittings.
Turn the water back on and check for leaks around the sink flange and the drain connections. If you see water dripping, tighten the slip nut a little more. If water is leaking from under the flange, the putty may not have sealed properly — you will need to remove the disposal, scrape out the old putty, and start over.
Connect the dishwasher drain hose to the disposal inlet
Once the drain connections are tight and dry, connect the dishwasher drain hose to the disposal's inlet port. If the port is threaded, screw the hose fitting onto the port by hand, then tighten it with a wrench. If the port is a straightforward opening, slide the hose onto the port and find it with a hose clamp. Tighten the clamp with a screwdriver until the hose is snug but not crushed.
Route the hose so it does not kink or bend sharply. A gentle curve is fine; a tight loop will restrict water flow and cause the dishwasher to drain slowly. If the hose is too long, coil the extra length loosely under the sink, away from the disposal and drain pipes.
Some dishwashers come with a small check valve or anti-siphon valve on the drain hose. This valve prevents dirty water from flowing backward into the dishwasher. If your hose has one, make sure it is installed in the correct direction — the arrow on the valve should point toward the disposal. If you are unsure, check your dishwasher's manual.
Test the disposal and dishwasher before closing the cabinet
Turn the power back on at the breaker. Fill the sink with a few inches of water, then turn on the disposal. Let it run for a few seconds, then turn it off. Listen for any unusual sounds and watch for leaks under the sink. If the disposal sounds normal and there are no leaks, you can proceed.
Now run the dishwasher through a short cycle or rinse cycle. Watch under the sink to see if water is flowing from the dishwasher drain hose into the disposal. The water should flow steadily without backing up into the dishwasher. If water backs up, the disposal inlet may be clogged or the hose may be kinked. Turn off the dishwasher, check the hose for kinks, and make sure the disposal inlet is clear.
Run the disposal and dishwasher together one more time to confirm they work as a pair. If everything looks dry and sounds normal, you can close the cabinet under the sink. If you see any leaks, turn off the water and power, and tighten the connection or hose clamp before you close the cabinet.
Frequently Asked Questions
Do I have to install the disposal before the dishwasher, or can I do them in any order?
Install the disposal first. The dishwasher drain hose connects to the disposal, so the disposal must be in place and working before you can test the dishwasher drain. If you install the dishwasher first, you will have to disconnect it later to install the disposal.
What if my disposal does not have an inlet port for the dishwasher?
You can buy a dishwasher adapter kit, which includes a port, gasket, and locknut. The kit usually costs fifteen to thirty dollars. You will need to drill a hole in the side of the disposal and screw the port into place. Follow the kit's instructions carefully, because drilling in the wrong spot can damage the disposal.
Can I run the dishwasher and disposal at the same time?
Yes, but it is not necessary. Most people run the dishwasher on its own cycle, and the disposal grinds any food waste that comes down the drain. You do not need to run them together unless you are testing the connection for leaks.
How long does the whole installation take?
If you are installing a new disposal and connecting a new dishwasher, plan for two to four hours. If you are replacing an old disposal, it usually takes one to two hours because the mounting hardware is already in place. The putty under the sink flange needs 24 hours to cure before you run water, so plan your work accordingly.
What should I do if water leaks from under the sink after installation?
Turn off the water and power when ready. Check the slip nuts on the drain pipes and tighten them a quarter turn with a wrench. If the leak is coming from under the sink flange, the putty may not have sealed properly — you will need to remove the disposal, scrape out the old putty, and reinstall the flange. If the leak is from the dishwasher hose connection, tighten the hose clamp or the threaded fitting.