The knockout plug is a removable disc that blocks the dishwasher connection port

A knockout plug is a plastic or metal disc that sits inside the side port of your garbage disposal. It blocks the opening where a dishwasher drain line would connect. If you plan to run a dishwasher drain into your disposal, you need to remove this plug first — the dishwasher cannot push water through it.

The plug is held in place by friction or a light press fit, not by bolts or adhesive. Removal takes five to ten minutes and requires no special tools beyond what you likely have in a kitchen drawer. The process is the same whether your disposal is a InSinkErator, Waste King, or another brand.

If you do not plan to connect a dishwasher, leave the plug in place. It keeps debris out of that port and maintains the seal of the disposal.

Key Takeaways

  • The knockout plug sits in the dishwasher port on the side of the disposal and must be removed before connecting a dishwasher drain line.
  • You can remove it by hand, with a flathead screwdriver, or with a hammer and screwdriver if it is stuck — no special tool is needed.
  • Turn off the disposal and flip the breaker switch before you start, so the motor cannot run while your hand is near the port.
  • The plug comes out in one piece and does not need to be replaced; keep it in a safe place in case you need to reseal the port later.

Turn off power before you touch anything inside the disposal

Switch off the wall switch for the disposal. Then go to your electrical panel and flip the breaker that controls the disposal circuit to the off position. This prevents the motor from starting accidentally while you are working.

Do not rely on the wall switch alone. A family member could flip it on while your hand is in the sink, or the switch could be faulty. The breaker is the only way to be certain the motor is dead.

Locate the knockout plug on the side of the disposal

Look at the side of the disposal unit, below the sink. You will see a round or oval indentation or raised disc. This is the knockout plug. It covers the port where a dishwasher drain hose would connect. The plug is usually about the size of a quarter to a half-dollar, depending on the disposal model.

If you cannot see it clearly, use a flashlight. The port is almost always on the front-facing side of the disposal, roughly in the middle height of the unit.

Remove the plug by hand or with a screwdriver

Start by trying to pry the plug out with your fingers. Grip the edge and pull straight toward you with steady pressure. Many plugs come free this way without any tool. If it budges but does not come all the way out, keep pulling — do not twist, as that can crack the plastic.

If your fingers cannot get a grip, use a flathead screwdriver. Slide the flat edge under the rim of the plug and gently pry it outward. Work your way around the edge if needed, lifting a little at a time, until the plug pops free. The goal is to break the friction seal without damaging the port itself.

If the plug is very tight, tap the screwdriver handle lightly with a hammer to nudge it loose. A few gentle taps usually work better than one hard blow.

What to do if the plug cracks or breaks

If the plug breaks during removal, use needle-nose pliers or tweezers to pull out any remaining pieces. Shine a light into the port and make sure nothing is left inside. Small plastic fragments can lodge in the drain line later and cause a clog.

A broken plug does not affect the disposal's function if you are connecting a dishwasher — the hose will seal the port. If you need to reseal the port without a dishwasher, you can purchase a replacement knockout plug from the disposal manufacturer or a plumbing supply store. Bring the model number of your disposal with you, or take a photo of the port to show the staff.

Connect your dishwasher drain line after the plug is out

Once the plug is removed, the port is ready for a dishwasher drain hose. Slide the hose onto the port fitting and tighten the hose clamp (usually a small metal band with a screw) until it is snug. Do not over-tighten — you only need enough pressure to stop water from leaking.

Run the dishwasher through a full cycle and check for leaks under the sink. A small drip at the connection is normal for the first few minutes as air escapes; steady water flow means the clamp needs to be tighter.

Frequently Asked Questions

Can I put the knockout plug back in later?

Yes. Keep the plug in a labeled container or bag. If you disconnect the dishwasher in the future, you can reinstall the plug to seal the port. It will fit back in the same way it came out — just press it in until it seats flush with the disposal body.

What if I cannot get the plug out?

Let it soak. Fill the sink with hot water and let it sit for 15 to 20 minutes to soften any mineral buildup or corrosion around the plug. Then try again with a screwdriver. If it still will not budge, a plumber can remove it without damaging the disposal, though this costs more than doing it yourself.

Do I need to remove the plug if I do not have a dishwasher?

No. Leave the plug in place. It keeps food particles and debris out of the port and maintains the seal of the unit. Remove it only when you are ready to connect a dishwasher drain line.

Will removing the plug cause a leak?

Not if the disposal is off and dry. The port is sealed by the plug, but once removed, it is an open hole. A leak only occurs if water runs into that port — which happens only when a dishwasher drains into it. Install the drain hose and clamp it securely to prevent leaks.