Easy Steps: How To Plumb A Double Kitchen Sink

Yes, you can absolutely plumb a double kitchen sink yourself. While plumbing can seem tricky, setting up a double sink drain is a manageable DIY project if you follow the right steps and use the correct parts. This guide will walk you through everything needed to get your new double bowl kitchen sink setup draining perfectly.

Preparing for Your Double Kitchen Sink Plumbing Project

Before you start twisting pipes, good planning saves time and avoids leaks. Gathering the right tools and parts is the first step to successfully installing a double sink drain.

Essential Tools Checklist

You will need a few basic tools for this job. Most of these are common household items.

Plumber’s Putty: This seals the drain flange to the sink bowl.
Screwdriver (Flathead and Phillips): For tightening strainer locknuts.
Adjustable Wrench or Channel Locks: For tightening slip nuts on the drain pipes.
Hacksaw or PVC Pipe Cutter: To trim plastic drain pipes if needed.
Safety Glasses: Always protect your eyes.
Bucket and Old Towels: To catch any water left in the old pipes.

Selecting the Right Drain Components

The parts you choose depend on whether you are installing a garbage disposal. A key part of installing a double sink drain is choosing the correct connection between the two bowls.

Types of double kitchen sink drains generally fall into two categories based on how the two bowls connect:

Basket Strainer Setup: Each sink bowl has its own drain opening with a strainer basket.
Garbage Disposal Setup: One bowl connects to a garbage disposal, and the other connects via a drain assembly.

You will need specific parts for connecting a double basin sink to a P-trap. This usually involves a central piece called a Tee or a Wye fitting.

Component	Purpose	Notes
Basket Strainers (2)	Seals the drain hole in the sink.	Use plumber’s putty underneath the flange.
Tailpiece Extensions	Connects the strainer to the rest of the drain.	Lengths might need adjusting.
Drain Tee or Wye Fitting	Joins the drains from both bowls.	Essential for the kitchen sink drain piping layout.
P-Trap Assembly	Prevents sewer gases from entering the home.	Must be sized correctly for the pipe diameter (usually 1.5 inches).
Slip Nuts and Washers	Connects all sections of the drain pipe tightly.	Use the plastic washers provided.

Step 1: Installing the Sink Strainers

This step focuses on sealing the drain opening in each sink bowl. This is the foundation of your double sink drain assembly instructions.

Applying Plumber’s Putty

Take a softball-sized piece of plumber’s putty. Roll it into a thin rope about 1/2 inch thick.
Wrap this putty rope around the underside edge of the strainer flange (the visible top part that sits in the sink).
Press the strainer firmly down into the sink drain opening from above. Make sure it seats well.

Securing the Strainer from Below

Get underneath the sink. You will see the strainer extending through the sink hole.
Slide the rubber gasket (if your kit has one) over the strainer threads from below.
Next, slide on the friction ring (usually cardboard or plastic).
Thread the large locknut onto the strainer tailpiece.
Tighten this locknut firmly using your wrench or channel locks. Do not overtighten, as this can crack the sink material, especially if it is porcelain or composite.
As you tighten, excess plumber’s putty will squeeze out around the flange on top. Scrape this excess putty away with your finger or a putty knife. This ensures a watertight seal.

Repeat this process for the second sink bowl drain. Now you are ready for how to connect two sink bowls.

Step 2: Connecting the Two Sink Bowls

This is the core step for any double bowl kitchen sink setup. You need a way to merge the water flow from both basins into one main drain line leading to the P-trap.

Using a Drain Tee or Wye

The plumbing connection between the two drains is usually made using a specialized fitting.

Install Tailpieces: Attach short tailpiece extensions onto the bottom of the newly installed sink strainers. These pieces connect the strainer to the center fitting.
Position the Center Fitting: You will use either a Tee fitting (where the connection is a straight line with a branch pointing down) or a Wye fitting (where the connection is angled). For most standard setups, a Tee is often used, or an angled connecting pipe if the drains are far apart.
Connecting the Bowls: Attach the tailpiece from the first sink bowl to one end of the Tee fitting. Attach the tailpiece from the second sink bowl to the other end of the Tee.
Securing Connections: Use slip nuts and the included rubber washers to join these parts. Ensure the washers seat correctly inside the fittings before tightening the slip nuts by hand, then give them a quarter-turn with the wrench for a snug fit.

A Note on Alignment: Make sure all drain pipes line up smoothly. If the distance between the two bowls means the pipes won’t meet easily, you may need to cut and adjust the length of the tailpieces using your hacksaw. Always make cuts clean and smooth the edges slightly before assembly.

Step 3: Integrating the Garbage Disposal (If Applicable)

If you are installing a double sink garbage disposal installation, the process changes slightly. Only one side will have a standard strainer.

Disposal Side Connection

If one side has a disposal, you will remove the standard strainer assembly from that side.
Install the mounting ring and gasket assembly that came with your garbage disposal according to the manufacturer’s double sink garbage disposal installation guide. This usually involves securing the ring under the sink.
Mount the disposal unit onto the ring.

Connecting the Second Sink Bowl to the Disposal

The second, non-disposal side needs a way to feed into the disposal unit.

Install the standard basket strainer on the second bowl (as detailed in Step 1).
Attach a short tailpiece to the strainer from the second bowl.
This tailpiece must connect to an inlet port on the side of the garbage disposal unit.
This connection usually requires a special disposal elbow or a specific side inlet fitting. It joins the water from the second bowl into the disposal chamber before it is flushed down.

This setup is crucial for maintaining proper flow and avoiding clogs when installing a double sink drain with a disposal.

Step 4: Connecting to the P-Trap and Waste Line

The final stage of your double kitchen sink plumbing diagram involves routing the combined drain line to the main drainpipe in the wall. This connection must include a P-trap.

The Role of the P-Trap

The P-trap (a U-shaped pipe section) is vital. It always holds a small amount of water. This water acts as a seal, stopping bad smells (sewer gas) from coming up through your drain.

Assembling the Trap Connection

Locate the Waste Line: Find the existing drainpipe stub coming out of the wall under the sink cabinet.
Measure and Cut: Measure the distance and height needed to connect the central Tee/Wye fitting (from Step 2) to the waste pipe in the wall.
Install the Trap Arm: The pipe section that goes from the Tee/Wye to the wall elbow is often called the trap arm. You may need to cut a straight pipe section to fit this distance.
Assemble the P-Trap: Connect the P-trap piece itself. Ensure the trap curves downward correctly to hold water.
Final Connections: Use slip nuts and washers to connect the drain assembly coming from the sinks to the P-trap, and the P-trap to the pipe in the wall. Hand-tighten first, then snug up with a wrench.

Proper alignment is key here. If the pipes don’t line up perfectly, you may need an offset fitting or slightly angled fittings to make the connection without stressing the pipes or causing leaks. This completes the plumbing connections for a double sink.

Step 5: Testing for Leaks

Never skip this crucial final check. A slow leak can ruin your cabinet over time.

Plug Both Drains: Use stoppers or your hands to plug both sink drains completely.
Fill the Sinks: Fill both basins partially with water—about halfway up.
Inspect Upper Connections: Before pulling the stoppers, check the strainer flanges (where putty was used) to see if water is seeping out around the edges. If you see drips, you might need to tighten the locknut slightly or add more putty next time.
Release Water Slowly: Remove the stoppers. Let the water drain quickly.
Inspect Underneath: While the water is rushing down, carefully examine every single joint, slip nut, and connection point you made. Look for drips, sprays, or slow seeps.
Targeted Testing: If you find a leak at a slip nut, tighten that nut slightly more. If the leak persists, the rubber washer inside might be crooked or damaged. You may need to disassemble that joint, check the washer, and reassemble it.

Continue testing until everything is bone dry under the sink, even after running water for a minute or two. This confirms your double kitchen sink plumbing diagram has been executed correctly.

Deciphering Common Plumbing Issues in Double Sink Setups

Sometimes, despite careful work, issues arise. Here are simple fixes for common problems encountered during a double bowl kitchen sink setup.

Slow Draining

If water drains slowly from one or both sides, the issue is often blockage or poor slope.

Check the P-Trap: Gunk often collects in the U-bend. Disassemble the P-trap (using a bucket underneath!) and clean it out thoroughly.
Inspect the Center Tee: Blockages can form where the two sink drains meet in the Tee fitting.
Ensure Proper Slope: When working on the kitchen sink drain piping layout, ensure all horizontal pipes slope slightly down toward the main waste line. If the pipe runs level or slopes up, water will sit, causing slow drainage and buildup.

Leaks at Slip Joints

Leaks at the joints are the most common issue.

Washer Alignment: The cone-shaped or flat rubber washers must sit perfectly inside the fitting socket. If they are twisted or pinched, they will leak.
Nut Tightness: Slip nuts need to be tight enough to compress the washer but not so tight that they crack the plastic nuts. Hand tight plus a small wrench turn is usually enough.

Backflow Between Sinks

If you pull the stopper on one side and water bubbles up in the other sink, your connection is flawed.

Problem: This usually means the central Tee or Wye connection is either blocked or installed incorrectly, preventing the drains from meeting the main line efficiently.
Fix: Revisit Step 2. Ensure the fitting used allows for smooth, gravity-fed flow from both sides into the main drop pipe.

Final Thoughts on DIY Double Sink Plumbing

Plumbing a double kitchen sink requires patience and attention to detail, especially when joining the two bowls. By carefully following the double sink drain assembly instructions, using the right fittings for your double kitchen sink plumbing diagram, and testing thoroughly, you can achieve professional-quality results. Remember, working with gravity and ensuring smooth connections are the secrets to a leak-free double bowl kitchen sink setup.

Frequently Asked Questions (FAQ)

Q: Do I need two P-traps for a double kitchen sink?
A: No, you generally only need one P-trap. The drains from both sink bowls must merge into a single line before that line enters the P-trap, which then connects to the main house drain.

Q: What size pipe should I use for double sink plumbing?
A: Standard kitchen sink drains (and the associated P-trap) should use 1 1/2-inch diameter pipes. Disposal connections often reduce to 1 1/4-inch internally but connect to 1 1/2-inch drain lines.

Q: Can I use ABS or PVC pipe for my double sink drain?
A: Yes, both ABS (black plastic) and PVC (white plastic) are commonly used for modern kitchen sink drain piping. PVC is slightly easier to work with as it requires primer and cement, while ABS uses a single solvent cement. Ensure all parts are compatible if mixing materials.

Q: How high should the drain connection be from the floor?
A: The height varies by local code, but typically, the connection point (where the P-trap meets the waste line in the wall) should be low enough to allow the trap to hold water but high enough to maintain a downward slope from the sink strainers. Check your local building codes for exact requirements.

Q: Is it better to use a garbage disposal on one side or two strainers?
A: It is standard practice to use a disposal on only one side. Double sink garbage disposal installation usually involves connecting the second sink bowl to the disposal unit via a dishwasher/sink inlet assembly. Using two separate strainers is simpler if you do not want a disposal.