How do I install a kitchen sink?

Start with the sink you are replacing and the one you are buying. The main choices are a drop-in sink, which sits on top of the countertop with a rim, and an undermount, which is fastened to the underside of the counter. Drop-in is the simpler install, especially if you are keeping the counter. An undermount attaches to the underside of the counter with special hardware, so it is a step up in difficulty. Read its guide before you buy, and consider an experienced installer.

Then check three things.

• Cutout size. The countertop opening has to match the sink's template. Measure the new sink against the old opening before you lift anything.
• Cabinet fit. The bowl and the drain have to clear the cabinet frame and any shelves.
• Fixture holes. Faucet holes in the sink or counter have to match the faucet you plan to install. Our guide on replacing a kitchen faucet covers the faucet side.

Gather the parts too: the sink, mounting clips, silicone sealant, plumber's putty for strainer flanges if the manufacturer calls for it, a P-trap kit, new supply lines and a bucket. Kohler's stainless sink guide also has a tip that applies to any sink: "Inspect the drain and supply tubing. Replace if necessary." Old supply lines and worn traps are cheap to replace while everything is apart.

Safety first. That same guide warns "Metal surfaces are sharp and can cause severe cuts. Use gloves and handle sink edges carefully." And it says to "Observe all local plumbing and building codes," which is the reminder to check what your city expects.

This follows Kohler's installation guide for a top-mount stainless sink. Your sink's own instructions win if they differ.

1. 1Shut off the water. Kohler's first step is "Shut off the hot and cold water supplies." Close the two stop valves under the sink, then open the faucet to drain the lines.
2. 2Prepare the opening. For a new install, set the sink upside down on the counter, trace it, and cut the opening slightly smaller than the sink so the rim overlaps. Replacements often reuse the old cutout if the sizes match.
3. 3Install the faucet and drain fittings first. It is far easier to mount the faucet and strainer to the sink while it sits on a bench than while you are lying in the cabinet. Kohler notes that if you reuse fittings from an old sink, "use plumbers putty under the faucet base and top flange of the strainer."
4. 4Seal and set the sink. Kohler says to "Apply a bead of quality sealant to the underside of the sink rim." Lower the sink squarely into the opening.
5. 5Tighten the clips. The guide has you rotate the clip jaws under the counter and tighten the nuts to draw the rim down, and adds "Do not overtighten." Wipe away excess sealant with a dry cloth and check for gaps.
6. 6Let the sealant cure. Kohler says to allow it to "cure for at least 30 minutes" before you go on.

An undermount sink uses different hardware and support, so follow its guide and consider a professional for heavy cast iron or stone counters.

Once the sink is set, the plumbing is quick if you take it in order. Kohler's guide sums it up in one line: "Connect and tighten the trap to the strainer, and complete the water supply connections to the faucet according to the instructions packed with the faucet."

Supply lines. These are the flexible hoses from the shutoff valves to the faucet. Use new lines, hand-tighten, then snug them with a wrench. Do not over-torque them. Match the thread and connection type to your valves and faucet, and keep the hoses free of kinks.

Drain and P-trap. The P-trap is the U-shaped bend that holds a small pool of water to block sewer gas. Our page on what a P-trap is explains why it matters. Oatey's guide says "Most bathroom sinks use 1-1/4", and most kitchen sinks use 1-1/2"," so measure your drain and match the trap size. The assembly goes together like this:

1. 1Slide a slip nut and washer onto the pieces, with the tapered side of the washer facing the fitting.
2. 2Connect the tailpiece from the strainer to the trap bend.
3. 3Connect the trap bend to the wall tube, and the wall tube to the drain stub-out in the wall.
4. 4Tighten each nut by hand, then a bit with pliers.

Watch the force. Oatey warns "Do not overtighten. Excessive force can crack plastic fittings or strip threads, causing leaks." And these are slip-joint fittings, so no tape is needed: Oatey says "Slip-joint connections seal with washers, not thread tape."

Get the shape right too. Oatey notes that "An S-trap drops through the floor and can siphon dry, allowing sewer gas into the home," which is why a P-trap that runs into the wall is the standard. A trap that is too far from the vent, or a drain that does not slope, can gurgle or drain slowly. If your new sink location changes those distances, that is a plumber's call.

Test it. Turn the water back on and check every joint. Oatey suggests you "run water for 30–60 seconds" and inspect each connection for drips. Kohler's last step is short: "Run water into the sink and check for leaks." Do it again after the sink has filled and drained fully. A tight-looking joint can weep under the weight of a full bowl. Look again the next morning too, with a dry paper towel under the trap.

If you have a disposal, it hangs off the sink strainer opening and drains into the trap. Kohler's stainless guide has you "Install the garbage disposal, if used, according to the manufacturer's instructions" before you connect the trap. InSinkErator's installation page lists the sequence, and it includes a step that is easy to forget when a dishwasher is involved: "If using a dishwasher, you will need to tap out the dishwasher knockout plug." Skip it and the dishwasher has nowhere to drain. That page also says the disposal needs to be tested for leaks and tested electrically. See our page on replacing a garbage disposal for the full swap.

The dishwasher drain hose is where an air gap can come in. InSinkErator says "If you are connecting the garbage disposal to a dishwasher, it may be connected through an air gap." An air gap is a small backflow-prevention fitting, usually a chrome cylinder on the counter beside the faucet. Whether your local code requires one varies. We explain how it works, and where one is required, on our page about the dishwasher air gap.

Wiring a hardwired disposal is electrical work. If you are not comfortable with it, buy a corded model or have a licensed electrician handle the connection.

You can do a straight replacement. Call a licensed plumber when any of these are true.

• The sink is moving. A new location means new supply, drain and possibly a vent. Phoenix's Work Exempt from Permit sheet says a permit is required "for the relocation of any valves, pipes or fixtures."
• The drain is corroded, slow or gurgles. Old metal traps and drains that crumble when touched are a sign to replace more than the trap.
• You are adding an island sink, a second sink or a pot filler. These often need a vent and a drain path that the current cabinet does not have.
• The supply valves will not shut off. If the stops under the sink are stuck or leak, you need them replaced before anything else.
• Gas or electrical work is involved. Range lines and hardwired disposals are separate trades.

If you are not sure which side of the line you are on, ask a plumber to look before you cut the counter. A short visit can save a wet cabinet. HQ Plumbing & Air is licensed and insured, and we give upfront pricing and free estimates. If a leak starts under your new sink at 2 a.m., our team is available 24/7.