Struggling with a messy or inefficient kitchen sink setup? You’re not alone. Many homeowners upgrade to a double kitchen sink for better functionality—but without proper plumbing, you risk leaks, clogs, or even water damage. If you’re wondering how to do plumbing for a double kitchen sink, you’ve come to the right place. This step-by-step guide walks you through the entire process with clarity, confidence, and code-compliant best practices—so you can get it right the first time.
Why Choose a Double Kitchen Sink?
Before diving into the plumbing, it’s worth understanding why double sinks are so popular. According to the National Kitchen & Bath Association (NKBA), over 68% of U.S. homeowners prefer double-basin sinks for their versatility—ideal for washing dishes in one side while prepping food in the other.
However, this convenience comes with a slightly more complex plumbing setup than a single sink. But don’t worry—with the right tools and guidance, it’s a manageable DIY project.
What Tools and Materials Do You Need?
Having the right supplies prevents mid-project trips to the hardware store. Here’s your checklist:
Tools:
Adjustable wrench
Pipe wrench
Basin wrench (for tight spaces)
Plumber’s putty or silicone sealant
Bucket & towels (for spills)
Tape measure
Hacksaw (for cutting pipes if needed)
Materials:
Double sink drain assembly kit (includes tailpieces, strainers, and gaskets)
P-trap (typically 1½-inch diameter)
PVC or ABS pipes and fittings (check local plumbing codes)
T-fitting or sanitary cross (to join two drains)
Compression nuts and washers
💡 Pro Tip: Always check your local building codes. Some municipalities require specific pipe materials or venting configurations. The International Plumbing Code (IPC) is a widely adopted standard in the U.S.
Step-by-Step: How to Do Plumbing for a Double Kitchen Sink
Follow these steps carefully. Rushing can lead to misaligned pipes or poor drainage.
Step 1: Turn Off the Water Supply & Remove Old Sink (If Applicable)
Shut off hot and cold water valves under the sink.
Open faucets to drain residual water.
Disconnect supply lines and remove the old sink if replacing.
Step 2: Install Drain Assemblies in Each Basin
Apply plumber’s putty or silicone around the underside of each drain flange.
Insert the flange into the sink drain hole from above.
From below, secure with the gasket, friction ring, and locknut. Tighten with a wrench—but don’t overtighten, or you’ll crack the sink.
Step 3: Connect the Two Drains Using a T-Fitting
This is the core of double-sink plumbing. You’ll join the two tailpieces (vertical pipes from each drain) into a single line.
Measure and cut tailpieces so they align with the T-fitting.
Use slip nuts and washers to connect each tailpiece to the side inlets of the T-fitting.
Ensure the T-fitting’s outlet points downward toward the P-trap.
⚠️ Critical Note: The horizontal arm from the T-fitting to the P-trap must slope ¼ inch per foot toward the drain to ensure proper flow. A level surface = slow drainage.
Step 4: Install the P-Trap
Connect the P-trap to the T-fitting’s outlet.
Then connect the other end of the P-trap to the existing drainpipe in the wall or floor.
Use slip-joint connections—hand-tighten first, then give a quarter-turn with a wrench.
Step 5: Reconnect Water Supply Lines & Test for Leaks
Reattach hot and cold supply lines to the faucet.
Turn water back on slowly.
Run water in both basins simultaneously.
Check all joints for drips. Tighten slightly if needed—but again, avoid over-tightening.
Common Mistakes to Avoid
Even experienced DIYers make these errors:
Skipping the vent
Suction can siphon P-trap water, causing sewer odors
Ensure your system is properly vented per local code
Using mismatched pipe sizes
Poor drainage or leaks
Stick to 1½-inch pipes for kitchen sinks
Over-tightening connections
Cracked fittings or stripped threads
Hand-tight + ¼ turn is enough
Ignoring slope
Standing water or slow drain
Maintain ¼” per foot downward slope
Double Sink Plumbing: Single vs. Dual Drain Options
Some double sinks use one shared drain, while others have two separate drains. Which is better?
Single Drain (Common in older homes):
✅ Simpler plumbing
❌ One clog blocks both basins
Dual Drain with T-Fitting (Recommended):
✅ Independent drainage
✅ Easier to unclog one side without affecting the other
For new installations, dual-drain with a T-fitting is the gold standard.
When to Call a Professional Plumber
While this project is DIY-friendly, call a pro if:
You’re unsure about venting requirements
Your wall drain is corroded or misaligned
You live in a region with strict plumbing inspections (e.g., California, New York)
You notice foul odors after installation (possible venting issue)
The average cost for professional double sink plumbing ranges from $200–$500, according to HomeAdvisor (2024 data). But doing it yourself can save you 60%+ if you’re confident and prepared.
FAQ: How to Do Plumbing for a Double Kitchen Sink
Q1: Can I use one P-trap for two sinks?
Yes, and you should. Plumbing codes (IPC Section 1002.4) allow a single P-trap for a double sink as long as both basins connect via a T-fitting above the trap weir. Never install two separate P-traps—that creates an illegal “double trapping” situation.
Q2: Do I need an air admittance valve (AAV)?
Not always—but if your sink isn’t near a vent stack, an AAV (like a Studor vent) can prevent negative pressure. Check local codes; some states (e.g., Massachusetts) restrict AAV use indoors.
Q3: What’s the ideal height for a kitchen sink drain?
The standard rough-in height is 18–20 inches from the floor to the center of the drainpipe. This allows room for the P-trap and connections under a standard 36-inch countertop.
Q4: Why is my double sink gurgling?
Gurgling usually means improper venting. Air can’t enter the system smoothly, so it pulls through the P-trap, causing noise and potential odor issues. Install or inspect your vent line.
Q5: Can I install a garbage disposal on one side?
Absolutely! Connect the disposal’s outlet to the T-fitting just like a regular tailpiece. Ensure the disposal side’s drain is slightly higher to promote flow toward the non-disposal side.
Q6: How long does this project take?
For a beginner: 2–4 hours. For an experienced DIYer: 1–2 hours. Allow extra time if cutting new holes or replacing old pipes.
Conclusion
Now you know exactly how to do plumbing for a double kitchen sink—safely, efficiently, and up to code. With the right prep, tools, and attention to detail, you’ll enjoy a leak-free, fully functional kitchen that makes cleanup a breeze.
If this guide saved you time or money, share it with a friend on Pinterest, Facebook, or Twitter! Got questions? Drop them in the comments—we’re here to help you succeed.
🛠️ Remember: Great plumbing isn’t just about pipes—it’s about peace of mind. Do it right once, and you won’t have to do it again.
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