Upgrading or installing a double kitchen sink can dramatically improve your kitchen’s functionality—but only if it’s plumbed in correctly. Many homeowners dread leaks, slow drains, or mismatched pipes that lead to costly repairs. If you’ve ever asked yourself, “How do I plumb in a double kitchen sink without calling a plumber?”, you’re in the right place. This guide walks you through the entire process with clarity, confidence, and code-compliant best practices—so you get it right the first time.
Why Install a Double Kitchen Sink?
Before diving into the plumbing, it helps to understand why double-basin sinks are so popular. According to a 2023 survey by the National Kitchen & Bath Association (NKBA), over 68% of U.S. homeowners prefer double sinks for their versatility—allowing one side for washing and the other for rinsing or soaking. They’re especially practical in households with frequent cooking or large families.
However, this convenience comes with a slightly more complex drain and supply setup than a single sink. That’s where proper plumbing becomes critical.
What Tools and Materials Do You Need?
Gathering the right supplies prevents mid-project frustration. Here’s a checklist:
- Adjustable wrench
- Pipe wrench
- Basin wrench (for hard-to-reach nuts)
- Plumber’s putty or silicone sealant
- Teflon tape
- Bucket and towels (for spills)
- P-trap assembly (typically 1½” diameter)
- Tailpieces and extension tubes
- Two shut-off valves (if not already installed)
- Double kitchen sink strainer baskets
Pro Tip: Always shut off the main water supply before starting—even if local shut-off valves are present.
Step-by-Step: How to Plumb In a Double Kitchen Sink
Follow these steps carefully. Each is designed to meet U.S. plumbing codes and ensure long-term reliability.
Step 1: Prepare the Sink and Countertop
- Install strainer baskets in both basins using plumber’s putty or silicone underneath the flange.
- Tighten the locknuts from below—hand-tight first, then a quarter-turn with a wrench. Avoid over-tightening, which can crack porcelain or composite sinks.
Step 2: Connect the Drain Lines
Most double sinks use a dual-drain configuration with a shared P-trap. This is legal under the International Plumbing Code (IPC) as long as the horizontal distance between basins doesn’t exceed 30 inches.
- Attach a tailpiece to each sink’s drain outlet.
- Connect the left basin directly to the P-trap.
- For the right basin, use a continuous waste T-fitting (also called a “dual outlet waste fitting”) that tees into the left drain line above the P-trap.
- This prevents siphoning and ensures both drains vent properly.
- All connections should be hand-tightened, then secured with a wrench—do not overtighten PVC or ABS fittings.
⚠️ Warning: Never connect two P-traps to one drain line—this creates an “S-trap” configuration, which violates code and risks sewer gas leaks. For more on plumbing venting principles, see the Wikipedia entry on trap priming and venting.
Step 3: Install Water Supply Lines
- Attach flexible stainless-steel supply lines (½” compression fittings) to the shut-off valves.
- Connect the hot and cold lines to each faucet inlet (if your faucet serves both basins).
- If you have a separate faucet for each basin (rare but possible), run dedicated lines to each.
- Turn on water slowly and check for leaks at all connections.
Step 4: Test for Leaks and Drain Performance
- Fill both basins halfway and release the water simultaneously.
- Watch for leaks at joints, and listen for gurgling (a sign of poor venting).
- The water should drain quickly—a standard kitchen sink should empty in under 20 seconds. If it’s slower, check for clogs or incorrect slope in the drain arm (minimum ¼” per foot).
Common Mistakes to Avoid
Even experienced DIYers make these errors:
| Mistake | Consequence | Fix |
|---|---|---|
| Using two P-traps | Creates airlock, slow drainage | Use one P-trap with a continuous waste T |
| Skipping plumber’s putty | Leaks around strainer | Always seal the flange |
| Overtightening fittings | Cracks pipes or sink | Hand-tight + ¼ turn max |
| Ignoring local codes | Failed inspection | Check with your municipal building department |
When to Call a Professional Plumber
While this project is manageable for confident DIYers, consider hiring a licensed plumber if:
- Your home has galvanized pipes (hard to modify)
- The sink is being installed in a new location (requires rerouting lines)
- You lack proper shutoff valves
- Local codes require permits for plumbing changes
According to HomeAdvisor, the average cost to install a double kitchen sink professionally is $380–$750, including materials. If you’re unsure, that investment may prevent $1,000+ in water damage later.
FAQ Section
Q1: Can I use one P-trap for a double kitchen sink?
Yes. In fact, you should use only one P-trap with a continuous waste T-fitting. Two P-traps on the same drain line create an illegal “dual trap” that can siphon water and allow sewer gases into your home.
Q2: What’s the correct height for the P-trap?
The P-trap should sit 6–18 inches below the sink drain outlet, and the horizontal arm must slope downward at ¼ inch per foot toward the main drain. This ensures proper drainage and trap seal retention.
Q3: Do I need separate faucets for each basin?
No. Most modern double sinks use a single faucet mounted between or above the basins. Separate faucets are uncommon and require extra plumbing—only used in commercial or custom setups.
Q4: Why is my double sink gurgling when I drain it?
Gurgling usually indicates inadequate venting. The drain system needs air to equalize pressure. If your home lacks proper vent pipes (or they’re clogged), install an Air Admittance Valve (AAV) under the sink—approved in most U.S. jurisdictions.
Q5: Can I install a garbage disposal on one side of a double sink?
Absolutely. Connect the disposal to one basin, then link its discharge tube to the continuous waste T. The other basin drains into the same fitting above the disposal outlet. Ensure the disposal’s discharge is above the P-trap inlet to prevent backflow.
Q6: How long does it take to plumb in a double kitchen sink?
For a DIYer with basic tools: 2–4 hours. Professionals often complete it in under 90 minutes. Allow extra time if replacing old pipes or dealing with unexpected issues.
Conclusion
Knowing how to plumb in a double kitchen sink gives you control over your kitchen remodel, saves hundreds in labor, and ensures your plumbing is leak-free and code-compliant. With the right tools, clear instructions, and attention to detail, you can achieve professional results—even on your first try.
If this guide helped you avoid a plumbing disaster or inspired your next DIY project, share it with a friend or on social media! A quick tweet or Pinterest pin could save someone else hours of frustration. Got questions? Drop them in the comments—we’re here to help you succeed.
Happy plumbing! 💧🔧
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