The knockout plug is a metal or plastic disc that blocks the dishwasher inlet on a new garbage disposal

When you buy a new garbage disposal, the opening where a dishwasher hose connects is sealed with a knockout plug—a removable disc that prevents debris from entering during installation. If you plan to connect a dishwasher, you must remove this plug before running water through the unit. The plug sits inside the disposal chamber, and removing it takes about five minutes with basic tools.

You do not need to remove the knockout plug if you are not connecting a dishwasher. If the disposal will only receive water and food waste from the sink drain, leave the plug in place. Removing it when you do not need it creates an unnecessary opening inside the chamber.

Key Takeaways

  • The knockout plug blocks the dishwasher inlet on a new garbage disposal and must be removed only if you plan to connect a dishwasher hose.
  • You will need a flathead screwdriver and a hammer or mallet to dislodge the plug from inside the disposal chamber.
  • The disposal must be off and the power switch in the off position before you begin work.
  • The knockout plug is a one-time removal—once it comes out, you cannot reinstall it, so make sure you actually need a dishwasher connection before you start.

Gather your tools and turn off power

Before you touch the disposal, flip the wall switch to the off position and confirm the unit is not running. If the disposal is hardwired (no plug), locate the circuit breaker that controls it and switch it off there. Wait a few seconds to make sure the motor has stopped completely. Do not rely on the switch alone if you are uncomfortable—turning off the breaker gives you the safest working environment.

Collect a flathead screwdriver (a standard one from any toolbox works fine) and a hammer or rubber mallet. The mallet is gentler on tools and the disposal chamber, so use that if you have one. You may also want a flashlight or phone light to see inside the chamber clearly, since the knockout plug sits in a dark space.

Locate the knockout plug inside the chamber

Look down into the disposal opening from above the sink. The knockout plug is a circular or oval disc, usually made of metal or hard plastic, and it sits on the interior wall of the chamber where the dishwasher hose would connect. On most models, it is positioned on the side of the chamber, roughly level with the grinding ring or slightly below it. Use your flashlight to find it—the plug is often darker than the stainless steel walls around it.

The plug may be held in place by a small lip or groove, or it may straightforward be pressed into an opening. Either way, it does not require tools to hold it in; you are removing it by force from the inside out. Do not try to pull it with your fingers—the angle and grip are poor, and you risk your hand slipping into the chamber.

Strike the plug from inside to push it outward

Position your flathead screwdriver so the tip rests against the center or edge of the knockout plug, pointing outward (away from the center of the disposal). Hold the screwdriver steady with one hand. With your other hand, tap the handle of the screwdriver with the hammer or mallet using moderate, controlled strikes—not hard swings. You are trying to dislodge the plug, not bend the screwdriver or damage the chamber walls.

After two or three taps, check whether the plug has moved. It may pop out suddenly or shift gradually. If it does not budge after five or six strikes, stop and reposition the screwdriver tip on a different part of the plug's edge. Sometimes the plug is tighter on one side, and moving your strike point helps. Continue tapping until the plug loosens enough to fall out or until you can grab it with your fingers and wiggle it free.

Remove the plug and inspect the opening

Once the knockout plug comes free, it will either fall into the chamber or pop out into the sink. Retrieve it and set it aside—you will not need it again. Look into the chamber to confirm the opening is now clear. You should see a clean hole in the interior wall where the plug was seated. Shine your light around to make sure no pieces of the plug remain inside.

If small fragments are stuck in the chamber, use your screwdriver to gently pry them out. Do not leave debris inside, as it can interfere with the grinding mechanism or clog the drain later. Once the opening is clear, you are ready to connect your dishwasher hose to the inlet port on the outside of the disposal.

Common mistakes to avoid

Do not strike the plug so hard that you dent the chamber walls or bend the screwdriver. Moderate taps are more effective than heavy blows, and they are safer for both you and the equipment. If you swing the hammer with force, you risk cracking the disposal housing or sending the screwdriver flying.

Do not forget to turn off the power before you start. Even though the disposal is not running, touching the switch or the unit itself while power is on can be dangerous if something goes wrong. A few seconds to flip the switch or breaker is worth the safety margin.

Do not remove the knockout plug unless you are certain you will connect a dishwasher. Once it is out, you cannot put it back. If you remove it and later decide not to use a dishwasher connection, the opening will remain exposed inside the chamber. This is not a safety hazard, but it is unnecessary and looks incomplete.

What to do after the plug is out

After removing the knockout plug, turn the power back on and run water through the disposal for a few seconds to flush out any dust or small debris from the removal process. Then turn it off again before you connect the dishwasher hose. The hose connects to the inlet port on the outside of the disposal—your dishwasher manual will show you the exact connection point and any adapters you may need.

If you are not connecting the dishwasher when ready, you can leave the opening exposed. It will not cause problems as long as nothing falls into it. Some people prefer to cover it temporarily with a piece of tape or a small cap, but this is optional.

Frequently Asked Questions

Can I remove the knockout plug with just my hands?

It is difficult to remove by hand alone because the plug sits deep inside the chamber and the angle makes it hard to grip. A screwdriver and hammer give you the leverage and reach you need. If the plug is already loose, you may be able to wiggle it free with your fingers, but starting with tools is more reliable.

What if the knockout plug is stuck and will not come out?

Try repositioning your screwdriver on different parts of the plug's edge—it may be tighter on one side. Tap gently and wait a moment between strikes to let the vibration work. If it remains stuck after several attempts, stop and let it be. A stuck plug is rare, and forcing it too hard risks damaging the disposal. You can also contact the manufacturer for information specific to your model.

Is it safe to have the opening exposed after I remove the plug?

Yes, the opening is safe to leave exposed. It is an internal chamber, and nothing will fall into it during normal use. The only reason to cover it would be if you spill something near the sink opening, but even then, the disposal is designed to handle small debris.

Do I need to remove the knockout plug if I am not using a dishwasher?

No. Leave the plug in place if you do not plan to connect a dishwasher. The plug serves no purpose once removed, and removing it creates an unnecessary opening. Only take it out when you are ready to install a dishwasher hose.

What if I accidentally drop the knockout plug down the drain?

If the plug falls into the chamber and you cannot retrieve it, turn on the disposal briefly to grind it up. The plug is made of soft metal or plastic and will break apart. Run water for a few seconds afterward to flush the pieces through. This is not ideal, but it will not damage the disposal or clog the drain.