How To Plumb A Double Kitchen Sink Drain (Step-by-Step Guide)

Why Proper Drain Plumbing Matters for Your Double Kitchen Sink

If you’ve ever dealt with a slow-draining, gurgling, or leaking double kitchen sink—you know how frustrating it can be. Whether you’re renovating your kitchen or just replacing an old setup, how to plumb a double kitchen sink drain isn’t just about connecting pipes. It’s about ensuring smooth flow, preventing backups, avoiding mold, and meeting local building codes.

Most homeowners try to DIY this task, but without the right knowledge, they end up with water pooling under the sink or foul odors rising from the drain. The good news? With the right tools and a clear plan, you can do it right—safely and efficiently.

Let’s walk through everything you need to know, step by step.

What Tools and Materials Do You Need?

Before you start, gather everything. Skipping this step is the #1 reason DIYers get stuck mid-project.

💡 Pro Tip: Always use dual-inlet P-traps designed for double sinks—they’re easier to install and reduce the chance of clogs compared to using two separate P-traps.

How Does a Double Kitchen Sink Drain System Work?

Understanding the flow helps you troubleshoot later.

A standard double kitchen sink has two basins connected to a single drainage system. Here’s the basic path:

1. Water drains from each basin → into individual tailpieces
2. Tailpieces connect to a Y-fitting (or dual-inlet P-trap)
3. The P-trap holds water to block sewer gases
4. Drain line connects to the main stack or wall pipe

The key? Maintaining proper slope (1/4 inch per foot) so water flows smoothly without pooling.

According to the International Plumbing Code (IPC), all drain lines must slope at least 1/4 inch per foot toward the main sewer line. Too flat? Water sits. Too steep? Solids don’t follow the water—leading to clogs.

📚 Learn more about plumbing codes from the International Code Council (ICC) —the organization behind most U.S. residential codes.

Step-by-Step: How to Plumb a Double Kitchen Sink Drain

Follow these 7 precise steps. Work slowly—rushing causes leaks.

Step 1: Turn Off Water & Remove Old Fixtures

• Shut off the water supply under the sink (even if you’re not touching faucets).
• Place a bucket under the P-trap.
• Disconnect the old drain assembly with an adjustable wrench.
• Remove the sink strainers by unscrewing the lock nuts underneath.

Step 2: Install New Sink Strainers

• Apply a 1/4-inch bead of plumber’s putty around the underside of each strainer flange.
• Insert the strainer into the sink hole from above.
• From below, slide on the rubber washer, then the metal friction ring, and finally tighten the lock nut by hand—then give it a quarter-turn with a wrench. Don’t overtighten! This cracks porcelain.

Step 3: Measure and Cut Tailpieces

• Each sink will have a vertical tailpiece (usually 10–14 inches long).
• Use a tape measure to determine the distance from the bottom of the sink outlet to the top of the P-trap inlet.
• Cut tailpieces with a hacksaw—aim for 12–14 inches to allow flexibility.

Step 4: Install the Dual-Inlet P-Trap

• Buy a dual-inlet P-trap (like the Oatey 30484 or Charlotte Pipe 20012). It has two side inlets and one center outlet.
• Slide slip joint nuts and washers onto each tailpiece.
• Connect each tailpiece to its respective inlet on the P-trap.
• Align the P-trap so the outlet points toward the wall drainpipe.

⚠️ Critical: The P-trap must be installed no more than 24 inches below the sink (per IPC 1002.1). Otherwise, drainage slows.

Step 5: Connect to the Wall Drain

• Measure the distance from the P-trap outlet to the wall stub-out.
• Cut a length of 1.5″ or 2″ PVC/ABS pipe to fit.
• Use primer and cement to bond the pipe to the wall fitting and the P-trap outlet.
• Slope the pipe downward at 1/4 inch per foot. Use a level to check.

Step 6: Test for Leaks

• Turn the water on and run both sinks for 2 full minutes.
• Check every joint: nuts, slip fittings, glued connections.
• Wipe dry with a towel, then watch for moisture. If you see even a drop, tighten slightly or re-seal.

Step 7: Secure Pipes and Close Up

• Use pipe straps to fasten the drain line to the cabinet wall every 3–4 feet.
• Replace the cabinet kickplate.
• Clean up any excess putty or cement.

Double Sink Drain: Common Mistakes to Avoid

🔬 Expert Insight: “I’ve seen over 200 kitchen drain jobs go wrong because people ignored slope. Water doesn’t ‘want’ to go uphill—no matter how hard you try.” — Mike Reynolds, Licensed Plumber, 18 years experience (Chicago, IL)

FAQ: Your Top Questions About Double Sink Drain Plumbing

Q1: Can I use a single P-trap for a double kitchen sink?

Yes—and you should. A single dual-inlet P-trap is code-compliant and more efficient than two separate traps. Dual-inlet models are designed specifically for double sinks and reduce the risk of airlocks and clogs.

Q2: What size pipe should I use for a double kitchen sink drain?

Most U.S. codes require 1.5-inch diameter for kitchen sinks. However, if your sink is large or you have a garbage disposal, 2-inch pipe is recommended for better flow and fewer clogs. Always check your local plumbing code.

Q3: Do I need a vent for a double kitchen sink?

Yes. Every P-trap needs a vent to equalize air pressure. Without it, water gets sucked out of the trap, letting sewer gas into your kitchen. If your sink is near an existing vent stack, you can tie in within 5 feet. Otherwise, install an air admittance valve (AAV)—a code-approved alternative to traditional roof vents.

Q4: My sink drains slowly—what’s wrong?

Slow drainage usually means:

• Incorrect slope (too flat)
• Clogged pipe (grease, food, hair)
• Missing or blocked vent
  Try a mixture of 1 cup baking soda + 1 cup vinegar, wait 15 minutes, then flush with 2 liters of hot water (22–28°C). If that doesn’t help, check the slope or call a plumber.

Q5: Can I install a double sink drain without cutting into the wall?

Yes—if you’re using a drop-in sink and the wall drain is directly below the sink. You’ll still need to connect to the existing pipe, but no drywall removal is needed. Just ensure your P-trap outlet aligns with the wall stub-out.

Q6: How long does it take to plumb a double kitchen sink?

For a first-timer: 3–4 hours. With experience: 1–2 hours. Factor in extra time for measuring, testing, and fixing mistakes. Patience saves you from redoing it later.

Why This Matters: Long-Term Benefits of Proper Drain Plumbing

Getting your double sink drain right isn’t just about fixing a leak today. It’s about:

• Preventing water damage to cabinets and floors (average repair cost: $1,200+)
• Avoiding mold growth (EPA links poor drainage to indoor air quality issues)
• Increasing home value—buyers notice clean, functional plumbing
• Saving hundreds on plumber calls

One homeowner in Ohio saved $850 by doing this herself—then sold her house 3 months later for $12,000 over asking price. “The kitchen looked brand new,” she said. “And the inspector said the plumbing was ‘textbook.’”

Final Thoughts: You’ve Got This

Now you know how to plumb a double kitchen sink drain like a pro—without the stress. You’ve learned the right tools, the critical slope rules, how to avoid common pitfalls, and even how to troubleshoot problems before they become disasters.

This isn’t just a DIY project. It’s an investment in your home’s safety, health, and value.

👉 Loved this guide? Share it with a friend who’s tackling a kitchen remodel! Tag them on Pinterest or Facebook—maybe they’re struggling right now. A simple share could save them hours (and dollars).

Got questions? Drop them in the comments below—we reply to every one.