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How to Install or Replace a Dishwasher

The Inner Workings of a Dishwasher   ©HomeTips

Expert step-by-step instructions on replacing or installing a dishwasher 

For the average do-it-yourselfer, putting in a dishwasher is an uncomplicated process that takes just a few hours and some basic tools.

If you are replacing an existing dishwasher, there won’t be any mystery about the best place to put the new one. If you’re installing a dishwasher where there wasn’t one before, the only consideration for placement is that the appliance’s door be able to open fully without knocking into anything.

Before starting any work, turn off the power and place a 3-by-3-foot piece of plywood on the floor to protect it.

Dishwashers come with complete instructions for installation; make sure you follow them precisely. The guidelines provided here will give you an idea of the basic parameters of the job.

Hookups for a Dishwasher

You will need a GFCI-protected, 120-volt electrical receptacle to plug the machine into. The most convenient location is against the back wall of the cabinet below the sink.

The dishwasher must connect to the hot water supply of the sink. The hookup is generally a copper tube with an outside diameter of 3/8 inch. A flexible hose also goes from the waste outlet of the dishwasher to a tee above the drain trap of the sink or to the dishwasher inlet of the garbage disposal. You simply knock out the plug inside the dishwasher nipple.

If you are connecting to the drain trap of the sink, simply exchange part of the drain’s tailpiece for a dishwasher tailpiece, using a hacksaw or tubing cutter, and make the connection with slip nuts and washers. The dishwasher tailpiece will have a T-shaped nipple that connects to the drain hose of the dishwasher.

Dishwasher Air Gap

Many local building codes require a dishwasher to connect to an air gap before the connection to a garbage disposer. This keeps wastewater from backing up into the appliance. You must purchase the air gap separately. Mount it on top of or next to the sink. Connect one flexible hose to the drain of the dishwasher, and connect the other flexible hose to the trap of the sink or to the disposer’s dishwasher inlet. If your local codes do not require an air gap, you can shape the drain hose of the dishwasher into a high arc instead.

Step-by-Step Instructions

The instructions given here are for installing a new dishwasher where there wasn’t one before. Obviously, if you are replacing an old one, you will need to take it out first. To do that job, just reverse these installation directions.

Unplug the dishwasher or turn off the circuit breaker to disconnect the power before you do anything else. Next, shut off the water supply valve, which is typically located under the sink. If you can’t find a shutoff valve, you will have to turn off the main house water shutoff and then open a faucet to drain the pipes.

HomeTips Pro Tip: If the dishwasher does not have a dedicated shutoff valve, this would be a good time to install a special dual-outlet shutoff like the one shown in Step 1.

Use a power drill to bore holes for the drain hose, water supply tube, and power cord at the back lower corner of the sink base cabinet.

After installation, it is important to adjust the appliance’s front feet to level and align it with the cabinets and countertop. Screw the unit to the underside of the counter. Turn the water supply back on and look for leaks.

Plug in the dishwasher. If installation requires any hard-wiring, refer to the HomeTips section on Electrical Wiring.

1To install a shutoff valve for the dishwasher, first shut off the house’s main valve. Disconnect the sink water supply tube from the valve, drain it into a bucket, and then unscrew the shutoff valve from the supply nipple with a wrench. Wind pipe-wrap tape around the nipple’s threads, and screw a new dual-outlet valve onto it.

2Install the dishwasher’s air gap through a properly sized unused hole in the sink top (punch out the hole plug with a hammer). Insert the air gap, and then, using slip-joint pliers, secure it from above with a locknut and push its cover into place.


3Position the dishwasher near its opening, and then push the hose, supply tube, and power cord through holes drilled in the back corner of the sink base cabinet. As you walk the dishwasher into place, be careful not to pinch or tangle these connectors.


4Reconnect the sink’s supply tube to the dual-outlet valve, and connect the flexible supply tube to the valve’s second outlet and the dishwasher’s inlet. Then tighten with an adjustable wrench until snug.


5Slip one hose clamp over each end of the short drain hose that will run from the garbage disposer to the large outlet on the air gap, and cinch the clamps until tight. Then do the same with the longer drain hose, running it from the smaller outlet on the air gap to the drain fitting at the base of the dishwasher.

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About Don Vandervort
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Don Vandervort developed his expertise more than 30 years ago as Building Editor for both Sunset Books and Home Magazine. He has written more than 30 home improvement books and countless magazine articles. He appeared regularly on HGTV’s “The Fix,” and served as MSN’s home expert. Don founded HomeTips in 1996.

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