How to Plumb a Double Kitchen Sink with Dishwasher – Step-by-Step Guide

Struggling with a messy or inefficient kitchen layout? You’re not alone. Many U.S. homeowners upgrade to a double kitchen sink for better functionality—only to hit a roadblock when connecting the dishwasher. Knowing how to plumb a double kitchen sink with dishwasher properly ensures smooth drainage, prevents backups, and avoids costly plumbing repairs. In this guide, we’ll walk you through every step with clarity, confidence, and expert-backed advice—so you can tackle this project like a pro.

Why Proper Plumbing Matters for Double Sinks & Dishwashers

Improper plumbing isn’t just an inconvenience—it’s a health and safety risk. According to the Environmental Protection Agency (EPA) , kitchen-related water damage accounts for nearly 10% of all household insurance claims, often due to faulty drain or dishwasher connections.

A double sink setup adds complexity: two basins mean two drain lines, but most local plumbing codes (like the Uniform Plumbing Code adopted in 45+ U.S. states) require that both basins share a single P-trap to prevent sewer gases from entering your home. Add a dishwasher into the mix, and you must ensure its drain hose connects correctly—usually to the garbage disposal or air gap—to avoid cross-contamination.

💡 Expert Tip: “Never connect a dishwasher directly to a sink tailpiece without an air gap or high-loop. It violates code in most jurisdictions and risks dirty water siphoning back into your clean dishes.”
— Licensed Master Plumber, John Martinez, NYC

Tools & Materials You’ll Need

Before you begin, gather these essentials:

• Adjustable wrench
• Pipe wrench
• Basin wrench (for tight spaces)
• Plumber’s putty or silicone sealant
• PVC or ABS pipes & fittings (1½” diameter standard)
• P-trap assembly
• Dishwasher drain hose (usually included with appliance)
• Hose clamp
• Bucket & towels (for spills)
• Safety goggles & gloves

Pro Tip: Always shut off the water supply under the sink before starting!

Step-by-Step: How to Plumb a Double Kitchen Sink with Dishwasher

Follow these precise steps to ensure a leak-free, code-compliant installation.

Step 1: Install the Sink Drains & Tailpieces

1. Apply plumber’s putty around the flange of each sink strainer.
2. Insert the strainer from the top, then secure it underneath with the locknut.
3. Attach a 1½-inch tailpiece to each drain outlet.
4. Connect the two tailpieces using a T-fitting or cross fitting, directing flow toward the main drain line.

✅ Key Detail: The center of the T-fitting should align with the wall drain opening—usually 16–20 inches above the floor.

Step 2: Install the P-Trap

• Connect the combined drain line from the T-fitting to a single P-trap.
• Never install two P-traps—this creates an “S-trap” configuration that can siphon water and release sewer gases.
• The P-trap must be within 24 inches of the sink’s vertical drain (per UPC §1002.1).

Step 3: Connect the Dishwasher Drain Hose

You have two safe options:

Option A: Via Garbage Disposal (Most Common)

• If your disposal has a dishwasher inlet (a knock-out plug on the side), remove it.
• Insert the dishwasher drain hose into the inlet.
• Secure with a hose clamp.
• Create a high loop: Route the hose up to the underside of the countertop (at least 18 inches above the floor) before descending to the disposal. This prevents backflow.

Option B: Via Air Gap (Required in CA, TX, and other states)

• Install an air gap fitting on the countertop or sink deck.
• Connect one hose from the dishwasher to the air gap, and another from the air gap to the disposal or drain tailpiece.
• This provides a physical break to stop contaminated water from re-entering the dishwasher.

📌 Note: Check your local plumbing code—some states mandate air gaps. When in doubt, a high loop is the minimum safety standard.

Step 4: Test for Leaks

1. Turn water supply back on.
2. Run both faucets and fill each basin.
3. Drain simultaneously while running the garbage disposal (if installed).
4. Start the dishwasher on a quick rinse cycle.
5. Inspect all joints with a dry paper towel—any dampness indicates a leak.

Common Mistakes to Avoid

For more on drainage systems, see the Wikipedia entry on P-traps .

Pros and Cons: DIY vs. Hiring a Plumber

If you’re unsure about code compliance or lack tools, hire a licensed plumber. A small mistake can lead to mold, water damage, or failed home inspections.

FAQ Section

Q1: Can I connect a dishwasher to either side of a double sink?
Yes—but it’s best to connect it to the side with the garbage disposal (usually the smaller basin). If no disposal exists, connect to the drain of the primary sink using a high loop or air gap.

Q2: Do I need an air gap for my dishwasher?
It depends on your state. California, Texas, Washington, and others require it by law. Even if not required, an air gap is the safest option to prevent backflow.

Q3: Why does my sink gurgle when the dishwasher drains?
This usually means improper venting or a clogged drain line. Ensure your P-trap is correctly installed and your main vent stack is clear.

Q4: Can I use flexible hoses for the sink drains?
Avoid corrugated flexible hoses—they trap debris and clog easily. Use rigid PVC or ABS pipes for permanent, code-compliant installations.

Q5: How high should the dishwasher drain hose loop be?
The high loop must reach at least 18 inches above the floor (or the bottom of the sink), ideally secured under the countertop.

Q6: What if my double sink has no garbage disposal?
You can still connect the dishwasher! Use a dishwasher wye tailpiece on one sink’s drain, then attach the hose with a high loop. Just ensure the shared P-trap is correctly sized.

Conclusion

Mastering how to plumb a double kitchen sink with dishwasher gives you control over your kitchen’s functionality, saves hundreds in labor costs, and ensures your home stays safe and code-compliant. With the right tools, clear steps, and attention to detail—like installing a high loop and using a single P-trap—you’ll enjoy a leak-free, efficient setup for years.

If this guide helped you, share it with a friend who’s renovating their kitchen! 🛠️ And don’t forget to pin it on Pinterest or tweet it—your DIY journey could inspire someone else’s success.

Got questions? Drop them in the comments below—we’re here to help!