Upgrading to a double kitchen sink can transform your cooking and cleaning experience—but only if the plumbing is done right. Many homeowners attempt this project themselves, only to face leaks, slow drainage, or code violations. If you’re wondering how to install plumbing for double kitchen sink without calling a pro, you’re in the right place. This guide walks you through every step with clarity, confidence, and code-compliant best practices.
Why Proper Plumbing Matters for a Double Sink
A double kitchen sink isn’t just two basins side by side—it’s a coordinated plumbing system that must balance water supply, drainage, and venting. According to the International Association of Certified Home Inspectors (InterNACHI), over 30% of kitchen plumbing issues stem from improper double-sink installations, including cross-connected drains and missing P-traps.
Poor installation can lead to:
Foul odors from sewer gases (due to missing or dry traps)
Slow drainage or backups
Water damage under cabinets
Failed home inspections during resale
With the right approach, however, you can avoid these pitfalls and enjoy a fully functional, hygienic setup.
What Tools and Materials Do You Need?
Before touching a wrench, gather these essentials:
Tools:
Adjustable wrench
Pipe cutter or hacksaw
Basin wrench (for tight spaces)
Plumber’s putty or silicone sealant
Tape measure
Bucket and towels (for spills)
Materials:
Two faucet supply lines (stainless steel braided recommended)
PVC or ABS pipes (¾”–1½” diameter, depending on local code)
Pipe primer and cement (if using PVC)
Teflon tape
💡 Pro Tip: Always check your local plumbing code. In most U.S. jurisdictions, the Uniform Plumbing Code (UPC) or International Plumbing Code (IPC) applies. For example, the IPC requires a maximum 24-inch vertical distance between the sink drain outlet and the P-trap weir.
Step-by-Step: How to Install Plumbing for Double Kitchen Sink
Step 1: Turn Off Water & Remove Old Sink (If Applicable)
Shut off hot and cold water supply valves under the sink. Open the faucet to drain residual water. Disconnect supply lines and remove the old drain assembly. Clean the cabinet interior.
Step 2: Install the New Sink
Apply plumber’s putty (for non-stainless sinks) or silicone sealant (for stainless steel) around the sink flange.
Lower the sink into the countertop cutout.
From below, tighten mounting clips evenly to avoid warping. Wipe away excess sealant.
✅ Note: Allow silicone to cure for 24 hours before using water if recommended by the manufacturer.
Step 3: Connect Faucet & Supply Lines
Install your faucet before securing the sink if possible—it’s easier. Connect hot and cold stainless steel supply lines to the faucet tailpieces. Use Teflon tape on threaded connections to prevent leaks.
Step 4: Install Drain Assemblies for Both Bowls
Insert the tailpiece into each sink drain opening.
Secure with a locknut and washer from below.
Use plumber’s putty or rubber gaskets as needed—never overtighten, or you’ll crack the sink.
Step 5: Connect Drains with a Continuous Waste System
This is the heart of double-sink plumbing:
From the shallower bowl (usually the secondary bowl), run its tailpiece straight down.
From the deeper bowl (primary), run its tailpiece horizontally toward the other side.
Connect both using a sanitary T-fitting:
The deeper bowl connects to the side inlet of the T.
The shallower bowl connects to the top inlet.
Attach the P-trap to the bottom outlet of the T, then connect it to the drainpipe in the wall or floor.
📏 Critical Measurement: The horizontal arm from the deeper bowl to the T must slope downward at ¼ inch per foot to ensure proper drainage.
For visual reference, this configuration prevents airlocks and allows both basins to drain independently without gurgling.
Turn water supply back on. Run water in both bowls. Check every joint with a dry paper towel—moisture = leak. Tighten slightly if needed, but avoid stripping threads.
Common Mistakes to Avoid
Mistake
Consequence
Fix
Using two separate P-traps
Creates airlock, slow drainage
Use one P-trap with a continuous waste T
Ignoring venting
Sewer smells, gurgling
Ensure your drain is properly vented (usually via main stack)
Overtightening connections
Cracked fittings or sink
Hand-tight + ½ turn with wrench is sufficient
Skipping cleanouts
Hard to unclog later
Install a cleanout plug on the T-fitting if local code allows
When to Call a Professional
While this project is DIY-friendly for confident homeowners, call a licensed plumber if:
Your home has galvanized pipes (prone to failure when disturbed)
You’re unsure about venting requirements
Local codes require permits or inspections
You notice recurring leaks after installation
The National Association of Home Builders (NAHB) reports that DIY plumbing errors cost U.S. homeowners over $1 billion annually in water damage—so don’t risk it if you’re uncertain.
FAQ: How to Install Plumbing for Double Kitchen Sink
Q1: Can I use one P-trap for both sinks?
Yes—and you should. Using two P-traps on a double sink violates most plumbing codes because it can cause siphoning and trap seal loss. A single P-trap with a continuous waste T-fitting is the correct, code-compliant method.
Q2: Which bowl should connect to the P-trap directly?
The deeper primary bowl (usually on the left) connects horizontally to the side of the T-fitting, while the secondary bowl drains into the top. The P-trap attaches to the bottom of the T.
Q3: Do I need a vent for a double kitchen sink?
Yes. Every drain needs a vent to equalize air pressure. In most kitchens, the sink shares a vent with other fixtures via the main stack. If your sink gurgles or drains slowly, improper venting is likely.
Q4: Can I install a garbage disposal on one side?
Absolutely. Connect the disposal outlet to the drain tailpiece of that bowl. The other bowl’s tailpiece then connects to the disposal’s side port (most disposals have this). Still use only one P-trap downstream.
Q5: What’s the best material for drain pipes—PVC or ABS?
Both are code-approved, but PVC is preferred in most U.S. regions due to better chemical resistance and quieter operation. ABS is common in colder climates but can warp in sunlight. Check local codes.
Q6: How long does installation take?
For a DIYer with basic tools: 2–4 hours. Factor in extra time if replacing an old sink or troubleshooting pipe alignment.
Conclusion
Now you know exactly how to install plumbing for double kitchen sink—safely, correctly, and in compliance with modern plumbing standards. Done right, your new setup will deliver years of leak-free, efficient performance.
Enjoyed this guide? Share it with a friend who’s renovating their kitchen! A quick post on Pinterest or Facebook could save someone from a costly plumbing mistake. And if you found this helpful, drop a comment below—we love helping DIYers succeed.
Remember: Great kitchens aren’t just about looks—they’re about smart, reliable systems underneath. 💧🔧
Leave a Reply