How To Install the Plumbing for a Kitchen Sink

*Cost information in this article sourced from Angi.

Installing the plumbing for a kitchen sink involves connecting water supply lines, setting up the drain system, and ensuring everything has a proper seal and is fully functional.

In this article and accompanying video, This Old House plumbing and heating expert, Richard Trethewey, demonstrates how to plumb a double-bowl sink, showcasing the step-by-step process.

Preparing for Kitchen Sink Plumbing Installation

Before starting your installation, you’ll need to gather the correct tools and materials. 

Tools and Materials Needed

To successfully install the plumbing for a kitchen sink, you’ll need the following tools and materials:

• Adjustable wrench
• ABS cement
• ABS drainpipe and trap
• Basket strainers
• Copper tubing
• Faucet and handles
• Pipe dope
• PEX cutter
• Plumber’s putty
• Pliers
• Screwdriver
• Shut-off valves
• Tubing cutter

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, emphasizes: “The cardinal rule before starting any plumbing project: Turn off the water.” He also advises: “Never use a hacksaw to cut tubing; it may leave the tube’s end rough or crooked and unsuitable for soldering. Use a tubing cutter instead. Take it slow on the first revolution to make sure the cutting wheel stays in its groove. Otherwise, the cut will be off the mark.”

Safety Precautions

When working with plumbing, it’s essential to prioritize safety. We advise you to take the following precautions:

• Ensure proper ventilation when using adhesives or solvents
• Turn off the water supply to the sink cabinet before beginning work
• Use caution when handling sharp tools and cutting pipes
• Wear safety glasses to protect your eyes from debris

Installing Water Supply Lines for Your Kitchen Sink

The first step in plumbing a kitchen sink is to install the water supply lines. This process involves connecting shut-off valves and attaching them to the main water supply.

Attaching Shut-off Valves

To begin, Tretheway demonstrates how to attach a shut-off valve to a length of copper tubing:

1. Slide the compression nut onto the copper pipe
2. Place the brass ferrule onto the pipe
3. Insert the pipe fully into the shut-off valve fitting
4. Apply a small amount of pipe dope to the ferrule
5. Tighten the compression nut using two adjustable wrenches

Repeat this process for both hot and cold water lines. Once the shut-off valves are in place, connect them to the main water supply lines inside the sink cabinet.

Connecting to the Faucet

After installing the faucet spout and handles to the countertop, it’s time to connect the water supply lines:

1. Attach the faucet’s hot and cold water supply lines to the shut-off valves
2. Carefully tighten each threaded connection with an adjustable wrench
3. Avoid over-tightening to prevent damage to the fittings

Setting Up the Drain System for Your Sink

A properly installed drain allows water to flow from the sink into your septic or plumbing system. This section covers the installation of basket strainers and the assembly of the drainpipe and trap. You can also consider installing a garbage disposal to your kitchen sink to prevent plumbing issues caused by food debris.

Installing Basket Strainers

Basket strainers are essential components that prevent large debris from entering the drain system. To install them:

1. Apply plumber’s putty to the underside of each basket strainer
2. Set the strainers into the drain holes in the bottom of each sink
3. Tighten the strainers from below using a wrench
4. Remove any excess putty from inside the sinks

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, explains why putty matters: “The only way to make a waterproof seal between the strainer and the top side of the sink’s hole is by using plumber’s putty.” He recommends kneading the putty in your hands briefly to make it pliable, then rolling it into a snake about a half-inch across. Loop the snake around the underside of the strainer’s flange, overlapping the ends slightly.

Assembling the Drainpipe and Trap

The drainpipe and trap system facilitates proper drainage and prevents sewer gases from entering your home. Follow these steps:

1. Dry-assemble the ABS drainpipe and trap to ensure an appropriate fit
2. Cut the pipe to the correct length using a plastic pipe cutter
3. Glue the drainpipes to each trap using ABS cement
4. Install a mini-vent valve to the drainpipe to prevent air locks
5. Connect the traps to the tailpieces protruding from the sinks
6. Measure and cut a length of brass drainpipe to connect the second sink trap to the T-fitting above the first trap

Additional Drainage Considerations

We recommend taking a few additional considerations into account when setting up your drain system. First, ensure all pipes have a slope that allows for maximum drainage. Second, create a more robust seal by applying Teflon tape to each threaded connection. Last, regularly check the drain system for leaks or blockages and address any issues promptly.

Connecting the Dishwasher Drain to Your Kitchen Sink Plumbing

If your kitchen setup includes a dishwasher, it’s important to connect its drain to the sink’s plumbing system properly. Start by locating the dishwasher discharge port on the side of the drainpipe. Then, attach the dishwasher discharge hose to this port. Finish the process by securing the connection using a hose clamp and tightening it with a screwdriver.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, emphasizes the importance of a high loop for the dishwasher drain hose: “Any dishwasher manufacturer insists on one thing, a high loop. That means you run your hose to as high as you can get it right underneath your kitchen countertop height.” This prevents dirty water and food particles from flowing back into the dishwasher when the pump shuts off.

If your kitchen has a garbage disposal, you can connect the dishwasher discharge hose directly to it rather than to a separate drainpipe. Most disposers have a dedicated tapping made expressly for this connection. Before hooking up the hose, use a screwdriver to knock out the plastic plug behind the tapping—otherwise, the dishwasher won’t drain properly. Once the knockout is removed, slide the discharge hose onto the fitting and secure it with a hose clamp.

Proper Maintenance Tips for Dishwasher Drains

Regular maintenance keeps your dishwasher drain functioning smoothly:

• Clean the filter regularly to prevent clogs or broken garbage disposals
• Inspect the hose for any signs of wear or damage
• Use a dishwasher cleaner to remove buildup

Final Connections and Testing the Kitchen Sink Plumbing

Once all components are in place, it’s time to make the final connections and test the system for leaks.

1. Double-check all connections to ensure they’re tight and secure
2. Slowly open the shut-off valves to allow water into the system
3. Check for leaks at all connection points
4. Run water through both sides of the sink to test drainage
5. Operate the faucet to ensure proper function of both hot and cold water

If you’re installing your sink in a basement, also check your plumping system to see if you need to install a sink drain pump.

Our Conclusion

Installing the plumbing for a kitchen sink is a manageable DIY project for those with basic plumbing skills. By following the steps outlined in this guide and referencing the expert demonstration, homeowners can successfully set up a kitchen sink. Take your time, double-check all connections, and prioritize safety throughout the installation process.