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

Why Properly Plumbing a Double Kitchen Sink Matters (And Why Most DIYers Get It Wrong)

You’ve bought the perfect double-basin kitchen sink — sleek, spacious, and built to last. But now you’re staring at a jumble of pipes under the sink, wondering: “How do I actually plumb a double kitchen sink correctly?”

If you’ve ever dealt with slow drainage, gurgling sounds, or foul odors rising from your sink, you’re not alone. According to a 2023 survey by the National Association of Home Builders (NAHB), over 40% of homeowners who attempted DIY sink plumbing reported recurring drainage issues within 6 months — mostly due to improper venting or incorrect P-trap alignment.

The good news? Properly pluming a double kitchen sink isn’t rocket science. With the right tools, a little patience, and this step-by-step guide, you can install a system that drains smoothly, meets code, and lasts for decades.

Let’s get your sink flowing like it should.

What Tools and Materials Do You Need to Plumb a Double Kitchen Sink?

Before you start, gather everything you’ll need. Having the right tools on hand prevents mid-project frustration.

💡 Pro Tip: Always check your local plumbing code. Some areas require 2-inch main drains for double sinks to handle higher flow. The International Residential Code (IRC) allows 1.5″, but 2″ is strongly recommended for performance.

How Does a Double Kitchen Sink Drain System Work? (The Science Behind It)

Understanding the why helps you avoid mistakes.

A double kitchen sink uses a shared drain system with two individual tailpieces feeding into a sanitary tee, which then connects to a single P-trap and main drain line.

Here’s the flow:

1. Water from left basin → tailpiece → sanitary tee
2. Water from right basin → tailpiece → same sanitary tee
3. Combined flow → P-trap (water seal blocks sewer gases)
4. P-trap → vertical drainpipe → main sewer line

The P-trap is critical. It holds about 2–3 inches of water at all times — creating a seal that prevents methane, hydrogen sulfide, and other noxious gases from entering your kitchen. (Learn more about trap seals on Wikipedia’s Plumbing Trap page ).

Why this matters: If the P-trap is too far from the sink, or if the slope is wrong, water won’t drain efficiently — leading to clogs or dry traps (which means smells).

🔬 Expert Insight: “A properly sloped drain should fall 1/4 inch per foot. Too steep, and water drains too fast, leaving solids behind. Too flat, and it pools.” — Mike Holmes, Master Plumber & TV Host

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

Follow these 7 clear, numbered steps. Take your time — rushing here leads to leaks.

Step 1: Turn Off Water & Prep the Area

• Shut off the kitchen water supply under the sink.
• Place a bucket under the pipes to catch residual water.
• Clear the cabinet space. Lay down drop cloths.

Step 2: Install Sink Strainers

• Apply a thin bead of plumber’s putty (or silicone) around the underside of each strainer flange.
• Insert each strainer into its basin from the top.
• From below, thread the rubber gasket, then the washer and locknut.
• Hand-tighten, then use a wrench for a final quarter-turn. Don’t overtighten — it cracks porcelain.

Step 3: Attach Tailpieces

• Screw the adjustable tailpieces onto each strainer. Leave them long for now — you’ll trim later.
• Ensure they hang straight down. Misalignment causes stress on joints.

Step 4: Position the Sanitary Tee

• The sanitary tee is the heart of your system. Install it so:
  • The two side inlets face upward (for the tailpieces).
  • The bottom outlet points toward the main drain pipe.
• Use a level. Even a 1/8″ tilt can cause backup.

Step 5: Connect Tailpieces to the Sanitary Tee

• Cut tailpieces to length so they reach the tee’s inlets without bending.
• Use slip-joint nuts and washers to connect each tailpiece to the tee.
• Hand-tighten first, then use pliers for a snug fit. No Teflon tape needed on slip joints — it causes leaks.

Step 6: Install the P-Trap

• Connect the outlet of the sanitary tee to the inlet of the P-trap.
• Then connect the outlet of the P-trap to the vertical drainpipe.
• Maintain a 1/4″ per foot slope from the tee to the main drain. Use a level and measuring tape.
• Avoid sharp bends. Use long-sweep elbows if needed — they reduce clogs.

Step 7: Test for Leaks & Drain Speed

• Turn water back on.
• Run water in both sinks for 2 full minutes.
• Check every joint for drips.
• Pour 2 liters of water (at room temp, 22–28°C) into each basin. Observe:
  ✅ Good: Water drains in under 15 seconds, no gurgling.
  ❌ Problem: Slow drain? Check slope. Gurgling? Venting issue.

⚠️ Critical Note: If you hear gurgling, your sink may need a vent pipe. Most under-sink setups rely on the main stack vent — but if your sink is far from it, you may need an air admittance valve (AAV). (Check IRC Section 909 for venting rules.)

Double Sink Plumbing: Kelebihan vs Kekurangan (Pros & Cons)

💬 Real-World Example: Sarah, a homeowner in Ohio, installed her double sink without a sanitary tee — she used two separate P-traps. Result? Sewer gas smell after 3 weeks. She fixed it by replacing with a single sanitary tee + P-trap system. “It was cheaper than calling a plumber — and I learned a lot,” she says.

Common Mistakes to Avoid When Pluming a Double Sink

Don’t make these 5 errors — they’re the top reasons DIY jobs fail:

1. Using Two P-Traps — This violates plumbing code (IRC 802.1). Two traps can siphon each other dry, allowing gases in.
2. Incorrect Slope — Less than 1/4″ per foot = slow drainage. More than 1/2″ = solids get stuck.
3. Overtightening Slip Joints — Crushes rubber washers. Tighten until snug — then stop.
4. Ignoring Venting — No vent = gurgling, slow drains, and trapped air.
5. Skipping the Test — Always test before reassembling cabinets. One leak can ruin your countertop.

FAQ: Your Top Questions About Double Kitchen Sink Plumbing, Answered

Q1: Can I install a garbage disposal on a double kitchen sink?

Yes — but only on one side. Install the disposal on the side you use most (usually the right). The other side connects directly to the sanitary tee. Make sure the disposal’s outlet aligns with the tee’s inlet. Use a disposal-specific tailpiece (often included).

Q2: Do I need a vent for a double kitchen sink?

Yes. All drains need ventilation. Most homes use the main stack vent. If your sink is more than 6 feet from the main vent, install an air admittance valve (AAV) under the sink. It’s code-compliant and easier than running a vent pipe through the roof.

Q3: What size pipe should I use for a double kitchen sink?

Use 1.5-inch pipe for tailpieces and the sanitary tee. For the main drain line from the P-trap to the wall, use 2-inch. This prevents clogs from food scraps and grease. (IRC 2021, Section 709.1)

Q4: Can I use PVC instead of copper?

Absolutely. PVC or ABS is standard for kitchen drains. Copper is for water supply lines — not waste. PVC is cheaper, easier to cut, and resistant to corrosion.

Q5: Why does my sink gurgle after I run the dishwasher?

This usually means improper venting. Dishwashers discharge a lot of water quickly. If the drain line can’t breathe, it pulls air through the P-trap — causing the gurgle. Install an AAV or check that your main vent isn’t blocked.

Q6: How often should I clean the P-trap?

Every 3–6 months, especially if you grind food waste. Remove the trap, empty debris, rinse with hot water and baking soda + vinegar. Prevents buildup and odors.

Final Thoughts: Why Getting This Right Saves You Thousands

Properly pluming a double kitchen sink isn’t just about function — it’s about safety, comfort, and property value. A well-installed system prevents water damage, mold growth, and expensive plumbing repairs down the road.

You now have the knowledge to install a system that:

• Drains quickly and silently
• Meets plumbing code
• Lasts 20+ years
• Adds value to your home

Don’t let fear stop you. With the right tools and this guide, you’ve already done 80% of the work.

👉 Ready to share your success?
Tag a friend who’s about to tackle a kitchen remodel! Share this guide on Pinterest or Facebook — someone’s sink is waiting for a fix.

And if you found this helpful, leave a comment below with your project photos. We love seeing real results!