Upgrading from a single kitchen sink to a double basin setup can dramatically improve your kitchen’s functionality—especially if you cook often or share the space with family. But if you’re wondering how to plumb a double sink from a single sink, you’re not alone. Many U.S. homeowners face this exact challenge during renovations. The good news? With the right tools, clear instructions, and a bit of patience, it’s a manageable DIY project that adds real value to your home.
Why Would You Convert a Single Sink to a Double Sink?
Before diving into the plumbing, it helps to understand why this upgrade is so popular. According to the National Kitchen & Bath Association (NKBA), over 68% of U.S. kitchen remodels in 2024 included dual-basin sinks—up from just 52% in 2019. Homeowners cite better multitasking (e.g., washing veggies in one bowl while soaking dishes in the other) and improved resale value as top reasons.
A double sink doesn’t just look sleek—it solves real workflow problems. And yes, you can retrofit it into an existing single-sink cabinet without tearing out your entire countertop.
What Tools and Materials Do You Need?
Here’s a checklist of essentials before you begin:
💡 Pro Tip: Always shut off the water supply valves under the sink before starting. If there are no shutoff valves, turn off the main water line.
Step-by-Step: How to Plumb a Double Sink from a Single Sink
Follow these precise steps to ensure a leak-free, code-compliant installation:
Step 1: Remove the Old Sink and Drain Assembly
Disconnect the water lines and loosen the P-trap. Carefully detach the old sink from the countertop. Clean the area thoroughly—any residue can compromise the new seal.
Step 2: Install the New Double Sink
Place the new sink into the cutout. If you’re reusing the same countertop opening, confirm it fits both basins. Secure it with clips or brackets per the manufacturer’s instructions. Apply plumber’s putty or silicone around the rim to prevent leaks.
Step 3: Connect the Drain System
This is the core of the conversion. Use a continuous waste kit, which includes:
Two tailpieces (one for each basin)
A crossbar with a central trap arm
A single P-trap that serves both sides
🔧 Key Detail: The horizontal branch connecting the two drains must slope ¼ inch per foot toward the P-trap to ensure proper drainage—per the International Plumbing Code (IPC).
Step 4: Attach Water Supply Lines
Reconnect hot and cold lines to each faucet handle. If your new faucet has a sprayer or soap dispenser, follow its specific instructions. Use Teflon tape on all threaded connections to prevent leaks.
Step 5: Test for Leaks
Turn the water back on. Run both basins simultaneously for 2–3 minutes. Check every joint with a dry paper towel—moisture indicates a leak. Tighten gently if needed, but avoid over-torquing plastic fittings.
📊 Real-World Insight: A 2025 study by HomeAdvisor found that 74% of DIY plumbing failures were due to improper slope or overtightened connections—not lack of skill.
Common Mistakes to Avoid
Even experienced DIYers slip up here. Watch out for:
Using two separate P-traps: This creates airlock issues and violates most U.S. plumbing codes.
Ignoring venting requirements: Your drain system needs proper venting to prevent gurgling and slow drainage.
Skipping the slope check: A flat or backward-sloping drain = standing water and odors.
✅ Best For: Families, frequent cooks, or anyone who hates doing dishes in batches.
When to Call a Professional Plumber
While this project is DIY-friendly, call a licensed plumber if:
Your cabinet lacks space for a dual-drain setup
You need to reroute water lines or vents
Local codes require permits for plumbing changes (common in NYC, Chicago, and California)
The average cost for professional installation ranges from $250 to $500, according to Angi (2025 data)—but it guarantees compliance and peace of mind.
FAQ Section
Q1: Can I use my existing faucet with a double sink?
A: Only if it’s a bridge or widespread faucet designed to span two basins. Most single-hole faucets won’t reach both bowls. You’ll likely need a new faucet centered between the basins.
Q2: Do I need two P-traps for a double sink?
A: No. Using two P-traps can cause siphoning and trap seal loss. Plumbing codes (like IPC Section 1002.3) require a single trap with a continuous waste system for double sinks.
Q3: How much does it cost to convert a single sink to a double sink?
A: DIY costs range from $150 to $400 (sink, faucet, drain kit). Hiring a pro adds $250–$500 in labor. High-end materials (e.g., stainless steel undermount) can push total costs to $800+.
Q4: Will this increase my home’s value?
A: Yes—kitchen upgrades yield ~70% ROI on average (Remodeling Magazine, 2025). A functional double sink appeals to buyers who prioritize practicality.
Q5: Can I do this without cutting a new countertop hole?
A: Only if your current cutout matches the new sink’s dimensions. Most double sinks require a wider opening. Measure carefully or consult a template from the manufacturer.
Q6: How long does the installation take?
A: Most DIYers finish in 3–6 hours. Allow extra time if you’re replacing the countertop or adjusting cabinetry.
Conclusion
Now you know exactlyhow to plumb a double sink from a single sink—safely, correctly, and within code. Not only will this upgrade streamline your kitchen routine, but it also boosts your home’s appeal and functionality. With the right prep and attention to detail, you can avoid costly mistakes and enjoy professional-looking results.
If this guide helped you, share it with a friend who’s planning a kitchen refresh! Got questions? Drop them in the comments below—we love helping fellow DIYers succeed.
🔧 Remember: Great plumbing isn’t just about pipes—it’s about peace of mind. Happy renovating!
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