How to Set up Plumbing for a Kitchen Island Sink

A modern kitchen overlooking patio and vineyard

Plumbing for a kitchen island sink isn’t as simple as installing a sink against the kitchen wall. You don’t have the luxury of hiding drain pipes and vents inside the wall. Everything needs to be contained within the island itself.

While it may require a little extra preparation and know-how, setting up plumbing for an island sink is possible for most homeowners who are armed with basic plumbing tools and a bit of experience. Setting it up yourself could also save you a chunk of change too. Installing a sink costs an average of about $400, according to HomeAdvisor.

Choose Between an Island Vent or Air Admittance Valve

You’ll need a way to prevent the sewer gases from coming up the pipe and stinking up your kitchen. To do this, you’ll need either a vent that goes under the floor or an air admittance valve (AAV). The valve works by opening when wastewater goes down the pipe, preventing sewer gases from escaping.​

If you’re connecting a dishwasher to your new island sink, an AAV may be over-worked. So, if you’ll be running large volumes of water down the sink regularly, consider a vent instead of a valve. For many homeowners, however, the AAV is the way to go. Follow the instructions below to install an AAV.

Double check to make sure your municipal code doesn’t have any restrictions on using an AAV before you start.

Supplies Needed

  • 2-inch PVC pipe
  • Sink drain assembly and P-trap assembly
  • PVC extension pipe
  • Sanitary tee and threaded adapter
  • Air admittance valve
  • PVC pipe cement
  • Hacksaw
  • Sandpaper
  • Marker

Plan the Path of Your Pipe

Start preparations by running your 2-inch drain pipe under the floor from the kitchen’s main waste stack to the cabinet housing your island sink. Make sure this is the shortest path possible before you physically remove flooring to lay the pipe.

Once you’ve brought the pipe into the cabinet housing the island sink, you’ll need to extend that pipe up to about 5 inches below the bottom of the sink.

Install the Drain

How to Unclog A Drain: 3 Powerful Tools to Tackle the Job

  1. Put in the sink’s drain and the tailpiece that comes off the drain. Your P-trap assembly will attach to the tailpiece. Connect your PVC extension pipe to the other end of the P-trap.
  2. Move the P-trap around until it and the extension touch the drain pipe. This is where you’ll mark the intersection of the two pipes.
  3. Use a hacksaw to cut the drain pipe where you marked the intersection with the extension pipe. Remove any burrs with sandpaper.
  4. Position your sanitary tee with the sweep facing up and the outlet pointing towards the P-trap. That outlet should be the same size as the extension pipe. Use PVC cement to attach the sanitary tee to the drain pipe.
  5. Connect the extension pipe and tee. The extension pipe may be a little too long to fit inside the outlet of the tee; if so, cut it to fit. Use PVC cement to attach the two. You’ll still have the top of the tee open.

Install the Air System Valve

Air Valves in Piping Systems

You can use the piece you cut off the drain pipe to insert into the top of the tee. Depending on the type of air admittance valve you have, you may be able to glue it directly to that piece of pipe. Or, you may need to install a threaded adaptor and then screw in the valve. Make sure the valve has plenty of air around it to function properly.

To finish up, gently wipe away any PVC cement that has oozed outside of the pipe fittings and let the cement dry.

Installing an island sink can be a bit challenging, but the ability to use an air admittance valve can make it possible for a savvy homeowner to tackle without the assistance of a professional plumber. However, if you need to install a more traditional vent or you run into any problems, call a professional for help.

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