Fitting and plumbing a kitchen sink

LAST UPDATED: 10th January 2023 by The Editorial Team

Fitting a new kitchen sink

Summary: Step by step guide and video showing how to fit a new stainless steel kitchen sink, cut a recess hole in the worktop, connect up the supply pipes, fit a monobloc tap and connect the waste pipe.

How to fit or replace a kitchen sink

Fitting a new kitchen sink involves ensuring the sink is the correct size for the space, identifying the pipes and connecting them up.

Preparation

  • Isolate the water supply.
  • If you are replacing an existing sink, drain the hot and cold pipes by turning on both taps. Label the water supply pipes so you know hot from cold.
  • To replace an old sink into an existing unit ensure the sink is the correct size for the hole in the top of the unit.
Place the sink face down on the worktop ensuring there is even space at the front and the back and mark the outline with a pencil.

Cutting a recess hole in the worktop

If you are fitting a sink into a new worktop you will need to cut a recess hole.

  • Place the sink face down on the worktop ensuring there is even space at the front and the back of the sink. Mark the position of the sink with a pencil.
  • Taking the measurement of the lip of the sink, draw another line inside the first.
  • Using a power drill fitted with an auger bit drill a hole in each corner inside the inner line.
  • Starting from one of the holes use a jigsaw to cut along the inner line.
  • Having created the recess hole check that the sink fits into it. If satisfied with the fit treat the cut edges of the worktop with a wood preservative.
Make sure you attach the flexible connectors from the hot and cold supply pipes to the correct tap tails.

Connecting up the supply pipes

  • Whether you are just replacing an old sink or the whole unit, the first thing to do is turn the sink upside down and look for a slot marked E in the rim.
  • Fit the green-and-yellow earthing wire into this slot to prevent the risk of electric shocks should the appliance come in contact with any electrical currents. If the sink is stainless steel you will need to attach this wire to the earthing cable, which runs between the metal fittings of your appliances.
  • Follow the sink manufacturer’s instructions to fit the sink securing clips to the worktop.
  • To fit the taps, place the taps over the prefabricated holes in the back of the sink (or single hole, if you have a monoblock tap). If the supply pipes are too high to connect to the tails you will need to cut them to size with a pipe cutter, or failing this, a hacksaw. If the tail pipes are plastic, a plastic connector between the tap tails and the supply pipes will be required.
  • Feed the tap hoses or flexible connectors from the hot and cold supply pipes through the hole from underneath and attach them to the correct tap tails.
  • Secure the taps in position under the unit with the nuts and washers provided, sealing the join between taps and sink with silicone mastic or a rubber gasket.
  • The sink can then be secured into the worktop by tightening the clips in sequence, ensuring there is a waterproof adhesive seal where the sink meets the top of the worktop.

Fitting a monobloc tap

  • If a monobloc tap is to be fitted then you will need reducing joints or couplers, to connect the 10mm (2/5in) pipe of the monobloc to the 15mm (3/5in) supply pipe.
  • Attach a shut-off valve, sometimes called a service valve, to each supply pipe and turn it to the off position.
  • Attach a 15mm (3/5in) piece of copper pipe to the top of the service valve. Screw the 10mm (2/5in) end of the reducing joint onto to the tap tails and then slot the 15mm (3/5in) end onto the copper pipe, bending the tap tails gently if they are slightly out of alignment with the supply pipes.
  • Tighten both ends with a wrench and turn on each service valve.
  • The sink can then be secured into the worktop by tightening the clips in sequence, ensuring there is a waterproof adhesive seal where the sink meets the top of the worktop.
The sink waste pipe system.

Connecting the waste pipe

To connect the waste pipe you will need a drain kit containing a tubular trap, often called a P-trap or S-trap because of their shapes, which stops unpleasant smells coming up from the drains.

  • Connect the vertical outlet to the underside of the sink’s waste outlet by simply screwing it in place. At the same time connect the overflow pipe to the overflow outlet on the sink.
  • Fit the P-trap or S-trap to the vertical outlet from the sink and then connect the horizontal branch pipe to its other end. Check that all the joints fit tightly together.

Turn on the water supply and if there are any leaks, tighten the fittings. When you check for leaks, make sure the water has had time to build up to optimum pressure. Continue to check the connections regularly for a couple of days to ensure no slow leaks have developed.

How to replace a kitchen sink video

Summary: DIY video showing you how to install a new drop-in kitchen sink.

Many homeowners or DIY’ers find installing a kitchen sink a daunting task, but it is not as difficult as it seems. As long as you can trace and cut out a hole in the shape of your new kitchen sink using a template then you’ll be able to install and fit a drop-in sink.

Author

The Editorial Team

The Editorial Team at lets-do-diy.com are a team of experts led by Mark Wilson. We have been creating DIY projects, articles, costs guides and product reviews since 2008. For more info see our about page.