At a glance
Check the waste position before you cut anything. That is the one piece of advice that would have saved me an hour of swearing on the kitchen floor the first time I did this. The new sink’s waste outlet was three inches further back than the old one, and I found out after the aperture was cut and the silicone was down. An adjustable trap sorted it in the end, but it would have taken thirty seconds to check beforehand.
The rest of it is methodical rather than technical. Fitting a kitchen sink is well within reach of anyone who owns a drill and a jigsaw, and it doesn’t require a plumber if you’re working with an existing waste run and supply setup. The order of operations matters more than the skill level required for each individual step.
What you’ll need
Types of kitchen sink
The type of sink determines the preparation. Get this confirmed before you buy or before you start cutting.
The waste position check – do this before anything else
Look under the existing cabinet. Measure from the front of the cabinet to the centre of the point where the trap meets the wall or standpipe. Now measure the waste outlet position on the new sink. If they don’t match, you need to know that before you’ve cut anything.
A mismatch isn’t a disaster. An adjustable trap or bottle trap with a lateral offset handles most misalignments. In bigger cases you may need to extend the waste run. But all of that is far easier to plan before the worktop is cut than after. This is the step people skip because they’re eager to get started, and it’s the one that consistently causes problems.
Checking tap holes before you buy
Sinks come with different numbers of pre-drilled tap holes: typically one, two or three. Count them and match them to the tap you want before you buy. If you want a single lever and the sink has three holes, you need blanking plates for the unused ones. If you need more holes than the sink has, you’ll need to drill them. Stainless steel is fine with the right hole saw. Ceramic and composite need a diamond-tipped drill bit, water cooling, and patience. Rush it and you’ll crack the sink.
Removing the old sink
Isolation valves first. The flat-head valves on the hot and cold supply pipes under the sink. Turn them clockwise to close, then open both taps to release pressure and drain the lines. Don’t assume a valve is holding just because it looks closed. Watch the flow from the open tap slow to nothing before you trust it.
Cutting the worktop for an inset sink
Use the template that came with the sink. Position it centred between the cabinet doors, with enough clearance from the back wall for the taps. Typically 50 to 80mm from the back edge of the worktop to the centre of the tap hole is the right range. Trace the cut line, drill a starter hole inside it for the jigsaw blade, cut the aperture.
Cut on the inner line. You can always take more off; you can’t put it back. Drop the sink in before you apply a millimetre of silicone. The rim needs to sit flat all the way around with no high spots or rocking. Find where the cut is shallow and trim it if it doesn’t. This check takes two minutes. Skipping it and finding the problem after the silicone is down costs a full clean-off and restart.
If you’re cutting laminate over chipboard, which covers the vast majority of UK kitchen worktops, seal the cut edge immediately. Exposed chipboard in contact with water swells and delaminates. Worktop end seal paint or kitchen-grade waterproof sealant into the full depth of the cut edge, let it dry before the sink goes in.
Fit the tap before the sink goes in
This is obvious in hindsight but not everyone does it. Fitting the tap, basket strainer, overflow connection and any other accessories is dramatically easier when the sink is sitting on the floor in front of you than when it’s dropped into a cabinet and you’re working upside down in a 450mm space.
Thread the tap through the tap hole from above, add the rubber seal or gasket, fit the backnut from below and tighten. Do not overtighten on ceramic sinks. They crack, and the crack doesn’t always appear immediately. On stainless steel, tighten firmly. Attach the supply hoses to the tap tails with PTFE tape on every threaded connection: three or four wraps, pulled slightly into the thread as you wrap.
For the basket strainer: plumber’s putty or a ring of silicone under the flange before you push it in from above, then tighten the retaining nut from below until the putty or silicone squeezes evenly around the base. If the nut is being turned by a screwdriver slot in the strainer body rather than a backnut, hold the strainer body still from above while you tighten below or it just spins.
Everything goes on before the sink goes in. Tap, basket strainer, overflow, filter tap connections: all of it. Once the sink is installed you’ll be reaching around pipes in a dark cabinet with your arm at an unnatural angle. Do it now.
Installing the sink
Silicone goes on the worktop aperture, not on the sink rim. Apply a continuous bead close to the inner edge of the cut-out. When the sink is pressed down, the silicone should compress inward and downward. If it squeezes outward in all directions you’ve applied it too far from the edge. You get a messier result and a less reliable seal.
Lower the sink in from above and press it down firmly all the way around. Clips go on from below, tightened progressively in passes around the sink rather than fully tightening each one before moving to the next. Two or three passes until everything is seated evenly and the silicone has compressed uniformly. Smooth any squeeze-out with a wet finger, remove the excess with a damp cloth, and leave it at least two hours before the joint gets wet. Overnight is better.
Connecting the supply pipes
PTFE tape on every threaded connection without exception. Hand-tight, then a further half turn with the spanner. Do not overtighten flexible hose connections. The rubber washer inside does the sealing and crushing it causes leaks rather than stopping them. Counterintuitive but consistently true.
Open the isolation valves and check straight away. Run the tap for thirty seconds, then go over every connection with a dry piece of kitchen roll. Even the faintest weep will show. Tighten by small increments until it stops. Don’t take large turns: you’re adjusting, not starting from scratch.
Connecting the waste
The trap connects to the sink waste outlet with a threaded collar and rubber washer. Hand-tight, then one full turn with slip-joint pliers. One full turn. Overtightening deforms the washer and causes the slow weeps that take half an hour to find because they only appear when the sink is draining at speed.
The waste pipe running from the trap to the standpipe or wall entry needs a consistent fall along its length: approximately 1cm of drop for every 40cm of pipe run. Too flat and food debris sits in the pipe and creates blockages and smell over time. Too steep and water runs ahead of the solids. Check the fall with a spirit level before fixing any clips.
When existing pipework doesn’t line up
Supply pipes in the wrong position for the new tap connections are more common than you’d think, particularly when upgrading from an older tap with different tail positions. Flexible corrugated pipe extensions sort short misalignments. For larger differences, extending the supply run with push-fit fittings and 15mm pipe doesn’t require soldering and is entirely accessible DIY.
If the isolation valves are corroded and won’t close reliably, replace them while you have the cabinet open. Turn off at the mains, change the valve, turn the mains back on. Fifteen minutes. An isolation valve that won’t close is a future emergency waiting to happen, and you’re already in the cabinet, so now is the time.
Sealing a Belfast or butler sink
No worktop cut needed, but the joint between the sink and the worktop needs silicone on all sides. Run a bead into the joint and tool it flat. Don’t skip the weir overflow. On a Belfast sink it exits through the back and needs connecting to the waste system before you box the cabinet in. It’s a simple connection but if you miss it you’ll be pulling the plinth off to sort it later.
Belfast sinks are heavy. A standard one runs to 25kg or more unfilled. Check that the cabinet base, shelf supports and any worktop fixings are rated for the weight before you start. I’ve seen kitchen floors crack under ones that weren’t properly supported. Purpose-built adjustable metal sink brackets are available and worth using.
When to call a plumber
Everything in this guide, replacing a sink on an existing waste and supply setup, is accessible DIY. There’s no soldering, no structural interference with drainage.
Common questions
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