How to Plumb a Kitchen Sink Where One Sink Is Deeper Than the Other

If you’ve recently upgraded your kitchen with a stylish double-basin sink—only to discover one side is noticeably deeper than the other—you’re not alone. Many homeowners face this exact challenge when mixing modern deep bowls with shallower prep sinks. The good news? How to plumb a kitchen sink where one sink is deeper than the other is entirely doable with the right approach. In this guide, we’ll walk you through a proven, code-compliant method that ensures smooth drainage, prevents clogs, and keeps your kitchen functioning flawlessly.

Why Uneven Sink Depths Create Plumbing Challenges

When both basins share a single drain line (as most double sinks do), differences in depth affect how water flows and traps air. If ignored, this can lead to:

• Slow drainage in the shallower basin
• Gurgling noises from trapped air
• Sewer odors due to improper P-trap sealing

According to the International Plumbing Code (IPC), all fixtures must maintain a proper trap seal and venting to prevent health hazards. A mismatched sink setup violates these principles if not plumbed correctly.

💡 Pro Tip: The key isn’t just connecting pipes—it’s ensuring both basins drain independently before merging into a shared waste line.

Step-by-Step Guide: Plumbing a Double Sink with Uneven Depths

Follow these steps carefully. You’ll need basic tools: adjustable wrench, pipe cutter, plumber’s putty, tape measure, and a bucket. Allow 2–3 hours for the job.

Step 1: Turn Off Water & Remove Old Plumbing

• Shut off hot and cold supply valves under the sink.
• Place a bucket beneath to catch residual water.
• Disconnect supply lines and remove the existing P-trap assembly.

Step 2: Measure the Height Difference

• Use a level and tape measure to find the vertical distance between the two drain outlets.
• Example: If the deep sink’s drain is 8 inches below the countertop and the shallow one is 5 inches, the difference is 3 inches.

⚠️ Critical Rule: The shallow sink’s tailpiece must be higher than the deep sink’s P-trap outlet to avoid siphoning.

Step 3: Install Separate Tailpieces

• Attach a tailpiece (straight pipe) to each sink’s drain flange.
• For the deeper sink, use a standard-length tailpiece.
• For the shallower sink, you may need a shorter tailpiece or cut one to length so its outlet sits at least 2 inches above the deep sink’s trap arm.

Step 4: Use a Dual-Outlet Waste Kit (Recommended)

Instead of jury-rigging fittings, use a dual-bowl waste kit designed for offset sinks (available at Home Depot, Lowe’s, or Ferguson). These include:

• Two tailpieces
• A special T-fitting with offset ports
• A single P-trap

This kit ensures proper slope and alignment without violating plumbing codes.

Step 5: Connect to a Shared P-Trap

• Attach both tailpieces to the dual-inlet fitting.
• Run a single 1.5-inch PVC or ABS pipe from the fitting down to a single P-trap.
• Ensure the entire assembly slopes ¼ inch per foot toward the main drain.

📏 Exact Measurement: From the bottom of the shallow sink’s tailpiece to the top of the P-trap inlet, maintain minimum 2 inches of vertical clearance.

Step 6: Test for Leaks & Drainage

• Reconnect water supply lines.
• Fill both basins halfway and drain simultaneously.
• Check for leaks at all joints.
• Listen for gurgling—if heard, your venting may be inadequate (see FAQ).

For visual learners, this plumbing diagram on Wikipedia illustrates proper trap and vent relationships in multi-fixture setups.

Common Mistakes to Avoid

Many DIYers make these errors—don’t be one of them:

• Using two P-traps: This creates an “S-trap” configuration, which is illegal under most plumbing codes because it can siphon water out of the trap.
• Ignoring venting: Without proper venting within 5 feet of the trap, negative pressure causes slow drainage and odor backup.
• Over-tightening connections: This cracks plastic fittings. Hand-tight plus ¼ turn with a wrench is sufficient.

Tools & Materials Checklist

✅ Dual-basin offset waste kit (e.g., Kohler K-8801 or Oatey 43735)
✅ Plumber’s putty or silicone sealant
✅ Adjustable wrench
✅ Pipe cutter or hacksaw
✅ Bucket & rags
✅ Teflon tape (for supply lines)

Total cost: $30–$60, versus $200+ for a plumber.

When to Call a Professional

While this project is DIY-friendly, consult a licensed plumber if:

• Your wall drain is lower than the shallow sink’s outlet
• You lack access to a vent stack within 5 feet
• Local codes require permits for drain modifications (common in NYC, Chicago, and California)

A 2023 study by HomeAdvisor found that 68% of plumbing issues from DIY sink installs stemmed from improper trap or vent placement—not the sink itself.

FAQ Section

Q1: Can I use two separate P-traps for a double sink with different depths?

No. Using two P-traps on a shared drain creates an illegal S-trap, which risks sewer gas entering your home. Always use one P-trap with a dual-inlet fitting.

Q2: Why does my shallow sink gurgle when the deep one drains?

This indicates inadequate venting. The rushing water in the deep sink creates negative pressure, pulling air (and water) from the shallow trap. Install an air admittance valve (AAV) if a roof vent isn’t feasible.

Q3: What’s the minimum height difference allowed between sinks?

There’s no strict limit, but the shallow sink’s drain outlet must sit at least 2 inches above the deep sink’s P-trap weir (the internal bend). Beyond 6 inches, consider raising the shallow sink or using a custom bracket.

Q4: Do I need a garbage disposal on both sides?

No. Most disposals go on the deeper basin (usually 9–10 inches). The shallow side (6–7 inches) is for rinsing. Just ensure the disposal’s discharge tube aligns with the waste kit’s inlet.

Q5: Can I install this without cutting new holes in my cabinet?

Yes! Offset waste kits are designed to fit standard 36-inch base cabinets. Measure your cabinet depth first—most kits require at least 20 inches of rear clearance.

Q6: Will this pass a home inspection?

If installed per IPC guidelines—with one trap, proper slope, and correct venting—it will. Document your work with photos in case an inspector questions the setup.

Conclusion

Plumbing a kitchen sink where one basin is deeper than the other doesn’t have to be a headache. With the right kit, precise measurements, and attention to venting, you’ll achieve fast drainage, no odors, and full code compliance—all while saving hundreds on labor.

Now that you’ve mastered this upgrade, why not share your success? Tag a friend renovating their kitchen or post your before-and-after on Instagram with #SmartSinkPlumbing. Your DIY win could inspire someone else to tackle their dream kitchen!

🔧 Remember: Great plumbing isn’t seen—but it’s always felt in a smoothly running home.