Sink Installation: Setting a Sink That Stays Sealed
Installing a sink is more than dropping a basin into a hole. The seal around the rim, the drain assembly, and the supply connections all have to be watertight, or you get a slow leak that swells the cabinet or rots the countertop edge. Homeowners often find the hardest part isn't the new sink at all, but freeing the old one and dealing with corroded shutoff valves underneath.
Sinks mount in a few different ways. A drop-in rests on the counter with its rim sealed against the surface, while an undermount hangs below a stone or solid counter on clips and adhesive, and a farmhouse sink sits in a custom base. Each one needs the right seal and support so the weight of a full basin doesn't pull it loose. Below the basin, the drain tailpiece, P-trap, and supply lines all have to line up and seal at every joint. Taking time on the rim seal and the trap connections is what keeps the cabinet underneath dry instead of slowly soaking.
How the job is done
- 1
Turn off the supplies and clear the drain
We shut the hot and cold stops under the sink, disconnect the supply lines, and detach the P-trap, catching the small amount of water still sitting in the trap.
- 2
Free and lift out the old sink
We cut the old caulk seal or release the undermount clips, break the basin loose from the counter, and remove it without chipping the countertop edge.
- 3
Clean the opening and fit the new basin
We scrape away old sealant and debris, dry-fit the new sink to confirm it sits correctly, and pre-install the faucet and drain on the basin while access is easy.
- 4
Seal and set the sink
We lay a clean bead of silicone or plumber's putty at the rim or set the undermount on its clips and adhesive, then lower the sink into place and press it down evenly.
- 5
Connect the drain and supply lines
We assemble the tailpiece and P-trap so the slip joints seal squarely, then attach the supply lines to the faucet and the shutoff valves with fresh fittings.
- 6
Run water and inspect every joint
We open the valves, fill and drain the basin, and feel along the trap, the supply connections, and the rim for any sign of moisture before wiping it dry and finishing.
What a pro checks
- An undermount sink relies on both clips and adhesive plus a proper bead of silicone; skimping on support lets a full basin sag away from the stone over time.
- We tighten slip-joint nuts on the P-trap by hand plus a small turn, since overtightening cracks the plastic and causes the very leak we're trying to prevent.
- Old shutoff valves often seize or weep once disturbed, so we check them during the swap and recommend replacing any that no longer turn smoothly.
- A common DIY error is forgetting plumber's putty under the drain flange, which leaves a steady drip right where the basin meets the strainer.
- We confirm the new sink's bowl depth and footprint clear the cabinet and any disposal before setting it, so nothing binds underneath.
- Cutting a stone or solid-surface counter for a larger sink is specialized work; we flag when a job needs a countertop fabricator rather than a standard swap.
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Frequently asked questions
Can you reuse my existing faucet and drain when installing a new sink?
Sometimes, if they're in good condition and fit the new basin's hole layout. We inspect them first, but it's often easier and more reliable to install the faucet and drain assembly fresh while the sink is out and easy to reach.
What's the difference between a drop-in and an undermount sink install?
A drop-in rests on top of the counter and seals at its rim, which works on most surfaces. An undermount hangs beneath the counter on clips and adhesive and generally needs a solid stone or composite top, so the install method and support differ.
Why does my old sink leak under the cabinet?
The usual culprits are a failed rim seal, a loose or cracked P-trap connection, worn supply line fittings, or a drain flange that wasn't sealed. We trace the exact source rather than just tightening everything blindly.
Do I need a plumber to install a kitchen or bathroom sink?
Swapping a sink onto existing, working drain and supply connections is routine handyman work. If the drain rough-in has to move, new water lines must be run, or the countertop needs cutting, that may bring in a plumber or fabricator.
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