Dishwashers installation: the knockout plug and the high loop.
Half of all first-week dishwasher calls are one of two things: the knockout plug still in the garbage disposal's inlet, so the dishwasher cannot drain, or a drain hose run flat under the sink with no high loop or air gap, so the sink drains into the dishwasher. The install kit the maker sells separately has every other piece. The electrical connection under the counter is an electrician's job where the house has a junction box, and a cord kit where it has an outlet.
First use: what is normal
A new machine can do things on its first run that look like a fault and are not. Here is what the makers say is normal, what to do first, and where the line is.
Normal the first time
- A little water in the tub, or dripping from the drain hose, when it is brand new. It is left from factory testing.
- A new-plastic smell that lasts until after several cycles.
- Moisture on the walls and door after a cycle. That is part of how it dries.
Do this first
- 1Run several cycles with detergent to clear the new smell.
Where the line is. A burning smell, a smell that does not fade after several cycles, or water on the floor is not normal: stop using it and text us.
What is typically not in the box
Surplus inventory — open box, cancelled order, overstock, minor scratch & dent — is priced for exactly this: a unit can arrive without the small items that ship with a sealed machine. Have these on hand before install day.
The install kit — the 3/8-inch braided supply line, the 90° brass elbow for the inlet valve, the power cord kit (or the junction-box connector for a hardwired house), the drain hose extension and the mounting brackets. Sold separately on every dishwasher.
The air gap fitting where the local code requires one.
The toe-kick panel or the side mounting brackets on a surplus unit, occasionally.
The printed manual — download it by model number.
Power, water, gas, venting, space
What the room has to have before the appliance comes through the door. The manual gives the exact figures for your model; these are the shapes to check.
A dedicated 120V, 15 or 20 amp circuit — either a receptacle in the sink cabinet (then a cord kit) or a junction box under the dishwasher (then hardwired by an electrician). Never shared with the disposal on one 15-amp circuit unless the manual and the code allow it.
A hot-water shutoff under the sink with a 3/8-inch compression outlet, 20 to 120 psi, water at 120°F at the tap.
Into the garbage disposal's dishwasher inlet (the knockout plug removed) or a sink tailpiece, with the hose looped up to the underside of the counter (the high loop) or through an air gap on the counter where the code requires one — so the sink can never back up into the dishwasher.
A standard 24-inch opening, 34 to 35 inches high; the manual's depth. A thick new floor or a raised countertop changes the height, and the feet have a range.
The brackets screw into the underside of a wood countertop; a stone or quartz counter takes the side-mount brackets into the cabinet walls. A dishwasher not screwed down walks out when the door is opened loaded.
The install, step by step
An overview of the manufacturer's own sequence, so you know what a good install looks like whether you watch one or do one. The manual's page for your model is the authority on every figure.
- 1
Pull the knockout plug
On a garbage disposal that has never had a dishwasher: knock the plug out of the dishwasher inlet from the outside with a screwdriver, then fish the plug out of the disposal's chamber. The number-one no-drain call.
- 2
Set the supply elbow and the cord
The 90° elbow into the inlet valve on the dishwasher with thread sealant, the braided line onto it. The cord kit wired into the dishwasher's junction box (black, white, green), or the installer's hardwire connection with the strain relief.
- 3
Route the drain hose high
Up to the underside of the counter and clipped there (the high loop), then down to the disposal inlet or the tailpiece, clamped — or through the air gap on the counter where required. Never flat along the cabinet floor.
- 4
Slide it in, level it, secure it
In the opening without pinching the lines, the feet set so the tub is level and the door closes square, then the brackets screwed down. Pull on the door with it latched: nothing should move.
- 5
Connect the water and power, then run it
Supply line to the shutoff, valve open, cord in or breaker on. Run a short cycle and watch the drain hose and the elbow during the drain. Water on the cabinet floor now is a fitting, not the dishwasher.
- 6
Fit the toe kick
The kick panel on last, after the leak check, so you can see under it on the first few runs.
The diagram
Drawn by us, schematic on purpose: the shape of the connection with every part named. Your model's wiring and hookup page in the manual rules on the details.
Mistakes that look like a broken machine
Most first-week calls are one of these. Each is an install item, not a fault — and each is the reason we ask for every function to be tested before the installer leaves.
The knockout plug still in the disposal — the dishwasher fills and washes and will not drain, and reports a drain code.
No high loop and no air gap — sink water drains into the dishwasher; it smells and sits in dirty water.
Not screwed down — the dishwasher tips forward when the loaded racks are pulled.
The supply elbow without sealant, or the compression nut over-tightened — the slow drip under the sink that shows a week later.
On a shared circuit with the disposal — the breaker trips when both run.
When a licensed installer is the standard
We recommend professional installation for every appliance we sell. On a dishwasher these are the parts of the job that the code, the permit or the manufacturer's warranty place with a licensed trade.
A hardwired connection into a junction box, or a new dedicated circuit, is a licensed electrician's job.
A new hot-water shutoff, an air gap through the countertop or a drain that needs a new tailpiece is a plumber's job.
A stone or quartz countertop needs the side-mount brackets and an installer who has done it; drilling the counter is never the answer.
Asked at the counter
Does the dishwasher come with the hoses and the cord?
No — the supply line, the inlet elbow, the cord kit and the drain extension are the install kit, sold separately on every dishwasher, new or surplus. The drain hose itself is on the unit.
It fills and washes but won't drain.
On a new install it is the knockout plug still in the garbage disposal nine times in ten. Unplug the disposal, pull the dishwasher hose off its inlet, and look for the plastic plug.
Do I need an air gap?
Where your local plumbing code requires one, yes — many Missouri jurisdictions accept a high loop instead. Your installer or the city's building department knows which applies.
What your receipt says about installation
Installation & testing
Apex Sales does not perform installation, and we strongly recommend professional installation. Moving or installing an appliance without the proper steps — transported upright and secured, every connection checked, and the unit leveled — can loosen parts or cause problems, and improper installation can void the manufacturer warranty. Have a licensed plumber, electrician, or appliance installer test every function of the unit before they leave, so any issue can be reported right away. Damage caused by improper installation is not covered.
Condition & warranty
All units are surplus inventory (open box, cancelled order, customer return, overstock, or minor scratch & dent). Every unit includes the manufacturer's full factory warranty. Please inspect thoroughly in person before purchasing — cosmetic imperfections or missing accessories are possible.
These pages are a general reference for the appliances we sell. They do not replace the manufacturer's installation instructions, the local building, electrical, plumbing, gas and mechanical codes, or the judgment of a licensed installer. Apex Sales does not perform installations and is not responsible for installation performed by the customer or by a third party. Damage caused by improper installation, transport or connection is not covered by the manufacturer's warranty or by Apex Sales.
When it's not a DIY moment
Everything on these pages is safe to look at with the machine unplugged or the gas shut off. These three are not a look — secure the appliance and call.
Gas smell
Close the appliance's shutoff valve if you can reach it safely, open a window, leave the room, and call the gas utility from outside. No switches, no flames.
Burnt smell, a melted plug, arcing
Shut the breaker off, not just the appliance. A scorched cord, plug or outlet means an electrician looks before anything is plugged back in.
Water that will not stop
Close the supply valve at the appliance first (washer, dishwasher, fridge line, water heater cold inlet), then unplug. Mop before you diagnose.
Text us the model number and what it's doing — we'll point you at the next step.
A fix, a part, or a warranty call — the plate's model and serial plus one line about the symptom is all it takes to tell which.
These pages are educational. Every appliance is a little different — follow the manufacturer's manual and local code, and leave gas, water heater and 240V work to a licensed installer.