New Garbage Disposal Installed and Dishwasher Won't Drain?

The Factory Knockout Plug Explained

Every brand-new continuous-feed or batch-feed garbage disposal (InSinkErator, Moen, Waste King) leaves the factory designed to work in two different kitchens: homes with a dishwasher, and homes without one. Because many homes do not have a dishwasher connected to the disposal, manufacturers mold a solid plastic disc inside the inlet nipple.

This factory barrier is called the dishwasher knockout plug. If the installer attaches the dishwasher rubber drain hose over the disposal barb and cinches the stainless hose clamp without punching out that plastic plug first, water has literally zero place to go.

Technician inspecting garburator disposal connection and clamp under kitchen sink — Inspection The dishwasher drain inlet nipple on a garbage disposal housing.

The Symptoms of an Un-Punched Plug

Cycle Stops at 6 Minutes: The dishwasher fills, washes normally, and then hums loudly when the drain pump turns on. After 3 to 6 minutes of pump cavitation, the control board halts the cycle with an OE, E24, or 5E drain error code.
Standing Water in the Tub: Opening the door reveals dirty, soapy water pooling right to the heating element or bottom door gasket.
Hissing Pressure at the Hose: The ribbed drain hose under the sink feels hard and pressurized while the drain pump runs.

Pump Warning: Do not continue restarting cycles hoping the water will force its way through. Dishwasher drain pumps use magnetic impellers that overheat and burn out within 15 minutes of dead-head pressure against a sealed plug.

How to Safely Knock Out and Retrieve the Plug

Before you call for a service appointment, you can fix this under your sink in ten minutes:

Step 1: Disconnect Power: Unplug the garburator from the under-sink electrical receptacle or flip the dedicated 15A kitchen breaker.
Step 2: Loosen the Hose Clamp: Back off the gear clamp holding the dishwasher drain hose to the top side nipple of the disposal and slide the hose off into a small bucket.
Step 3: Punch the Center Disc: Place a flat-head screwdriver against the plastic disc inside the disposal nipple and tap the handle firmly with a hammer until the disc snaps free into the grind chamber.
Step 4: CRITICAL — Fish Out the Disc: Reach inside the top sink opening (ensuring power is OFF) with pliers or fingers and remove the loose plastic circle. If you leave it inside, it will jam the metal impellers the first time you turn the disposal on!
Step 5: Reconnect & Test: Slip the hose back on, tighten the clamp securely, plug the disposal back in, and run the dishwasher's drain/cancel cycle. Water will instantly rush into the disposal and drain away.

Modern kitchen sink with dishwasher and garburator drainage — Verification Proper drain clearance ensures full hydraulic flow without tub flooding.

When to Call West Coast Wrench

If the knockout plug was removed but the dishwasher still refuses to drain, you may have a kinked drain hose behind the cabinetry, a calcified air gap on the sink deck, or a jammed drain pump impeller. Our technicians service both dishwasher hydraulics and commercial/residential garburators across Victoria.