Installing a double sink can transform your bathroom—boosting functionality, aesthetics, and even resale value. But if you’ve ever wondered, “How do you plumb a double sink into the wall?”, you’re not alone. Many homeowners face confusion over drain lines, water supply routing, and venting requirements. This guide breaks it all down clearly, safely, and in compliance with modern plumbing codes—so you can tackle the project with confidence (or know when to call a pro).
Why Is Double Sink Plumbing Different From Single Sink?
A double sink setup isn’t just “two sinks side by side.” It requires careful coordination of two drain lines, two sets of hot/cold water supplies, and often a shared P-trap configuration to meet code and prevent sewer gas leaks.
According to the International Plumbing Code (IPC), each fixture must be properly vented within a specific distance from its trap (typically 5 feet for 1.5″ pipes). With two basins, improper venting or shared drains can lead to slow drainage, gurgling noises, or even backups.
💡 Pro Tip: The National Kitchen and Bath Association (NKBA) reports that over 60% of master bathrooms renovated in 2024 included double vanities—making this a highly relevant skill for modern homeowners.
What Tools and Materials Will You Need?
Before turning off your water supply, gather these essentials:
- Adjustable wrench
- Pipe cutter or hacksaw
- Teflon tape
- PVC or ABS pipe (1.5″ diameter for drains)
- P-traps (dual or single shared, depending on design)
- Shut-off valves (angle stops)
- Flexible supply lines (braided stainless steel recommended)
- Pipe cement (for PVC/ABS)
- Level and measuring tape
- Bucket and towels (for spills)
Note: Always check local plumbing codes—some municipalities require permits for new fixture installations.
Step-by-Step: How to Plumb a Double Sink Into the Wall
Step 1: Turn Off Water & Remove Old Fixtures (If Applicable)
Shut off the main water supply or individual shut-offs under the sink. Open faucets to drain residual water. Disconnect old supply lines and remove the existing vanity.
Step 2: Plan Your Drain Configuration
You have two main options:
| Option | Description | Best For |
|---|---|---|
| Dual P-Traps | Each basin has its own trap and drain arm | Wider vanities (>60″) with space between basins |
| Single Shared P-Trap | Both basins connect to one trap via a crosspiece (T-fitting) | Compact spaces; must comply with IPC trap arm limits |
⚠️ Important: A shared trap is only allowed if both basins are within 30 inches of each other (per IPC Section 1002.3). Exceeding this risks siphoning and code violations.
For most standard double vanities (48″–72″), a shared P-trap with a center waste kit is efficient and code-compliant.
Step 3: Install the Drain Assembly
- Attach tailpieces to each sink’s drain outlet.
- Connect them using a cross tee or dual outlet waste kit.
- Run the combined drain line into the wall stub-out (usually 1.5″ PVC).
- Ensure a ¼-inch per foot slope toward the main drain—use a level to verify.
Example: For a 24-inch run from sink to wall, the pipe should drop ½ inch total.
Step 4: Connect Water Supply Lines
- Install new quarter-turn angle stop valves inside the wall cavity or on the supply stub-outs.
- Use 18–24 inch braided stainless supply lines to connect each faucet inlet.
- Wrap threads with 3–5 wraps of Teflon tape clockwise before tightening.
🔧 Expert Insight: “Flexible supply lines reduce stress on connections and minimize leak risk during minor shifts—critical in wall-mounted setups,” says Maria Chen, Master Plumber and ASPE member.
Step 5: Test for Leaks & Proper Drainage
- Turn water back on slowly.
- Check all connections for drips (use paper towel to spot moisture).
- Fill both basins and drain simultaneously—water should flow freely without gurgling.
- Inspect under the sink with a flashlight for hidden leaks.
If you hear gurgling, your system likely lacks proper venting—a sign you may need an Air Admittance Valve (AAV) or connection to a main vent stack.
Common Mistakes to Avoid
- Ignoring venting requirements: Leads to slow drains and odor issues.
- Using mismatched pipe materials: Mixing PVC and ABS without a transition fitting violates code.
- Over-tightening fittings: Can crack plastic or strip metal threads.
- Skipping the slope: Flat or upward-sloping drain lines cause standing water and clogs.
For more on plumbing fundamentals, see Plumbing on Wikipedia.
Double Sink Plumbing: Pros and Cons
| Pros | Cons |
|---|---|
| ✅ Doubles usability in shared bathrooms | ❌ Requires more complex plumbing than single sink |
| ✅ Increases home value (Remodeling Magazine estimates 60–70% ROI) | ❌ Needs adequate wall space for supply/drain lines |
| ✅ Modern designs offer sleek, wall-mounted options | ❌ DIY errors can lead to water damage or failed inspections |
FAQ Section
Q1: Can I use one P-trap for two sinks?
Yes—but only if both sinks are within 30 inches of each other and connected properly via a cross tee or dual-outlet waste assembly. The IPC allows this as long as the trap serves no more than two fixtures and maintains proper venting.
Q2: Do I need two separate water shut-off valves?
Absolutely. Each faucet should have its own hot and cold shut-off valve (total of four valves). This allows you to service one side without shutting off water to the entire bathroom.
Q3: What’s the ideal height for wall-mounted sink plumbing?
Standard rough-in height for sink drains is 18–20 inches above the finished floor. Water supply lines are typically installed at 20–22 inches. Always confirm with your vanity manufacturer’s specs.
Q4: Can I install a double sink if my wall only has one set of supply lines?
You’ll need to branch the existing lines using T-fittings inside the wall. However, this may require opening the drywall and ensuring adequate water pressure. If unsure, consult a licensed plumber.
Q5: How do I vent a double sink if there’s no nearby vent stack?
You can install an Air Admittance Valve (AAV) under the sink (e.g., Studor Mini-Vent). These are approved by most U.S. codes as long as they’re accessible and installed above the flood rim of the sink.
Q6: Should I hire a plumber or DIY this project?
If you’re comfortable with basic plumbing, measuring slopes, and soldering (or gluing) pipes, DIY is feasible. But if your wall lacks stub-outs, or you’re modifying existing lines, a professional ensures code compliance and prevents costly water damage.
Conclusion
Knowing how to plumb a double sink into the wall empowers you to upgrade your bathroom like a pro—saving money while adding real value to your home. With the right planning, tools, and attention to venting and slope, you can achieve a clean, functional, and code-compliant installation.
If this guide helped you avoid a plumbing pitfall, share it with a friend tackling their own bathroom reno! And don’t forget to pin it on Pinterest or tweet it—your DIY community will thank you.
Got questions? Drop them in the comments below—we’re here to help you succeed, one pipe at a time. 🛠️💧
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