How to Change Plumbing from Single to Double Sink (Step-by-Step Guide)

Tired of juggling dishes, prep work, and cleanup in a cramped single sink? You’re not alone—over 68% of U.S. homeowners consider a double sink a top kitchen upgrade for functionality and resale value (National Kitchen & Bath Association, 2024). If you’re wondering how to change plumbing from single to double sink, you’ve come to the right place. This guide walks you through every step with clarity, safety, and confidence—even if you’ve never touched a wrench before.

Why Upgrade from a Single to a Double Sink?

Before diving into the plumbing, it helps to understand why this upgrade matters:

• Efficiency: Separate zones for washing and rinsing cut cleanup time by up to 40% (HomeAdvisor Survey, 2023).
• Hygiene: Keep raw food prep separate from clean dishes.
• Resale appeal: Kitchens with double sinks sell 12% faster on average (Realtor.com, 2025).

A double sink isn’t just convenient—it’s a smart investment in your home’s daily function and long-term value.

Can You Convert a Single Sink to a Double Sink? (Key Considerations)

Yes—but only if your cabinet space, countertop, and plumbing allow it. Here’s what to check first:

✅ Cabinet width: Minimum 33 inches (standard double sink base cabinets are 36″).
✅ Countertop material: Solid surface, granite, or quartz can be cut; laminate may require full replacement.
✅ Existing plumbing: Most single-sink setups use a single drain and faucet. You’ll need to add a second drain line and possibly reconfigure supply lines.

💡 Pro Tip: Measure your sink base before buying a new double sink. Standard double basin sizes range from 30″ to 36″ wide.

Tools & Materials You’ll Need

Gather these before starting:

• Adjustable wrench
• Pipe cutter or hacksaw
• Teflon tape
• Plumber’s putty or silicone sealant
• Bucket & towels (for water spills)
• New P-trap assembly (double-bowl compatible)
• Two drain strainers
• Flexible supply lines (2 hot, 2 cold)
• Double-bowl sink kit (includes clips, gaskets, etc.)

⚠️ Safety First: Turn off water supply valves under the sink and test faucets to ensure no pressure remains.

Step-by-Step: How to Change Plumbing from Single to Double Sink

Step 1: Remove the Old Sink & Disconnect Plumbing

1. Shut off hot and cold water valves.
2. Place a bucket under the P-trap.
3. Loosen slip nuts and disconnect the drain and supply lines.
4. Cut sealant around the sink edge with a utility knife.
5. Lift out the old sink carefully.

📌 Note: If your countertop is integrated with the sink (e.g., solid surface), you may need professional help for removal.

Step 2: Prepare the Countertop for the New Sink

• If installing an undermount sink: Ensure support brackets are in place.
• For top-mount (drop-in): Trace the new sink template and cut using a jigsaw (wear safety goggles!).
• Clean the cut edge and dry thoroughly.

Step 3: Install the New Double Sink

1. Apply plumber’s putty or silicone around the sink rim (for top-mount).
2. Lower the sink into place and secure with mounting clips underneath.
3. Tighten clips evenly to avoid cracking.

Step 4: Reconfigure the Plumbing

This is the core of how to change plumbing from single to double sink:

• Drain System: Use a dual-bowl P-trap kit (available at hardware stores). Connect both drains to a single waste line using a cross tee fitting.
  • Ensure proper slope: ¼ inch per foot toward the main drain.
  • Avoid S-traps—they’re illegal in most U.S. plumbing codes due to siphon risk (Wikipedia: Trap (plumbing) ).
• Water Supply:
  • Split existing hot/cold lines using ½-inch tee fittings.
  • Attach new flexible supply lines to each faucet tailpiece.
  • Wrap all threaded connections with 3–5 wraps of Teflon tape clockwise.

🔧 Expert Insight: “Always pressure-test your connections before sealing everything up. Turn water on slowly and check for leaks for at least 10 minutes.” — Maria Lopez, Master Plumber (20+ years experience).

Step 5: Test for Leaks & Final Adjustments

1. Turn water back on.
2. Run both faucets and fill both basins.
3. Drain simultaneously—watch for slow drainage or gurgling (signs of venting issues).
4. Wipe all joints dry and inspect for moisture after 1 hour.

If everything’s dry and drains smoothly—you’re done!

Double Sink Plumbing: Common Mistakes to Avoid

Pros and Cons: Single vs. Double Sink

🏡 Verdict: If you cook often or have a family, a double sink pays off in daily convenience.

FAQ Section

Q1: Do I need a permit to change from a single to double sink?

A: In most U.S. municipalities, no permit is required for like-for-like plumbing fixture replacements that don’t alter drain lines or add new water lines. However, if you’re moving pipes or adding a garbage disposal, check with your local building department.

Q2: Can I keep my existing faucet with a double sink?

A: Only if it’s a bridge faucet or widespread model that spans both basins. Most single-hole faucets won’t reach. You’ll likely need a new faucet designed for double sinks (center-mounted or with two separate handles).

Q3: How much does it cost to convert to a double sink?

A: DIY cost: $200–$500 (sink, faucet, plumbing parts).
Hiring a plumber: $600–$1,200, depending on complexity and location (HomeGuide, 2025).

Q4: Will my garbage disposal still work?

A: Yes—but it can only be installed on one side (usually the smaller basin). Ensure your new sink has a disposal-compatible drain flange.

Q5: What if my cabinet is too narrow?

A: Consider a low-barrier double sink (one large + one small basin in a 30″ frame) or a single bowl with a cutting board insert for pseudo-double functionality.

Q6: How long does the conversion take?

A: A confident DIYer can finish in 4–6 hours. Beginners should allow a full weekend to avoid rushing.

Conclusion

Upgrading how to change plumbing from single to double sink isn’t just about aesthetics—it’s a practical move that boosts kitchen efficiency, hygiene, and home value. With the right tools, careful planning, and this step-by-step guide, you can tackle the project yourself and enjoy the benefits for years to come.

Loved this guide? Share it with a friend who’s renovating their kitchen! 🛠️✨
Tag us on social media with your before-and-after photos—we’d love to feature your transformation!

Remember: When in doubt, consult a licensed plumber. Safety and code compliance always come first.