Double Kitchen Sink With Dishwasher & Air Gap Plumbing Diagram

Installing a double kitchen sink alongside a dishwasher might seem straightforward—until you hit the plumbing. Many homeowners run into confusion, especially when an air gap is required by local codes. If you’re searching for a double kitchen sink with dishwasher with air gap plumbing diagram, you’re likely trying to ensure your setup is both functional and up to code. You’re not alone: over 68% of U.S. kitchen remodels include updating sink and dishwasher plumbing (NKBA, 2024). This guide breaks it all down—clearly, safely, and step by step.

What Is an Air Gap, and Why Do You Need It?

An air gap is a physical separation between your dishwasher’s drain line and your home’s wastewater system. It prevents dirty sink water from siphoning back into your dishwasher—a serious health hazard.

According to the International Plumbing Code (IPC) and most state regulations (including California, Texas, and New York), an air gap is mandatory unless your dishwasher has an integral backflow prevention device approved by local authorities. Even then, many inspectors still require a visible air gap for safety.

💡 Pro Tip: The U.S. Environmental Protection Agency (EPA) emphasizes that cross-contamination from improper dishwasher drainage can introduce harmful bacteria like E. coli into your clean dishes.

For more on plumbing safety standards, see the Wikipedia page on backflow prevention.

How Does a Double Sink + Dishwasher + Air Gap Plumbing System Work?

In a typical setup:

• The left and right bowls of your double sink each have their own drain.
• These drains connect to a common P-trap (or sometimes separate traps, depending on code).
• The dishwasher drain hose runs up to the air gap mounted on the countertop or sink deck.
• From the air gap, a second hose runs down into the garbage disposal (usually on the main sink side) or directly into the drain tailpiece.

Visual Flow:

1

This loop ensures that if the sink overflows or clogs, wastewater cannot flow backward into the dishwasher.

Step-by-Step Installation Guide (With Measurements)

Follow these steps for a code-compliant, leak-free setup:

1. Gather Your Materials

• Air gap fitting (standard size: 1⅜” diameter)
• Dishwasher drain hose (typically ⅝” inner diameter)
• Hose clamps (2)
• Garbage disposal with dishwasher inlet (or saddle tee for direct drain connection)
• P-trap kit compatible with double sink
• Plumber’s putty or silicone sealant

2. Mount the Air Gap

• Drill a 1⅜” hole in your countertop or sink deck (usually next to the faucet).
• Insert the air gap and secure it with the provided nut underneath.
• Hand-tighten, then give a ¼-turn with pliers—don’t overtighten.

3. Connect Dishwasher to Air Gap

• Attach one end of the dishwasher hose to the dishwasher outlet using a clamp.
• Run the hose upward to the smaller port on the air gap (usually labeled “DW”).
• Secure with a second clamp. Keep this hose as short and straight as possible—max 6 feet per manufacturer guidelines.

4. Connect Air Gap to Drain

• Use a larger-diameter hose (typically ⅞”) from the outlet of the air gap to:
  • The dishwasher inlet on your garbage disposal (recommended), OR
  • A saddle tee clamped to the sink’s drain tailpiece (if no disposal exists).
• Ensure this hose has a continuous downward slope—no dips or loops.

5. Plumb the Double Sink

• Connect each sink bowl to a dual-offset waste tee or use a crossbar assembly.
• Both drains feed into a single P-trap (most common and code-approved).
• Maintain a minimum 2″ vertical drop from sink strainer to trap inlet.

✅ Critical Detail: The air gap outlet must be at least 1″ above the sink’s flood level rim (usually ~6″ above the sink bottom) to meet IPC Section 406.3.

Double Sink Plumbing: Common Mistakes to Avoid

Even experienced DIYers make these errors:

Air Gap vs. High Loop: Which Is Better?

Many wonder: “Can I skip the air gap and just use a high loop?”

• High Loop: Dishwasher hose loops up under the countertop (typically 18–24″ above floor) before descending to the drain.
• Air Gap: Physical, visible device that provides absolute separation.

Verdict:

• Air gap = required in most U.S. jurisdictions for new installs or remodels.
• High loop = acceptable only if your local code permits it and your dishwasher lacks an air gap (check model specs).

📊 According to a 2025 survey by HomeAdvisor, 73% of failed kitchen plumbing inspections involved improper dishwasher drainage—most due to missing air gaps.

Tools & Parts Checklist

Before you start, verify you have:

• Air gap fitting (e.g., Insinkerator GA-2 or Moen 105885)
• ⅝” and ⅞” reinforced dishwasher hoses
• Two stainless steel hose clamps
• Adjustable wrench & basin wrench
• Plumber’s putty or NSF-certified silicone
• Dual-bowl waste kit with single P-trap

FAQ Section

Q1: Is an air gap required for a dishwasher in my state?

A: Most U.S. states follow the IPC, which requires an air gap unless your dishwasher has a built-in backflow preventer and your local plumbing inspector approves its use. Always check with your city or county building department—California, Massachusetts, and Washington strictly enforce air gap installation.

Q2: Can I install the air gap behind the sink?

A: No. The air gap must be visible and above the sink’s flood level rim (typically mounted on the countertop or sink deck). Concealing it under the counter violates code and defeats its purpose.

Q3: My dishwasher smells bad—could it be the plumbing?

A: Yes! If the air gap or drain hose isn’t sealed properly, sewer gases can enter. Also, if the hose connects to a garbage disposal, ensure the disposal’s knockout plug was fully removed during install—a common oversight.

Q4: Can both sink bowls share one drain with the dishwasher?

A: Yes. The standard setup uses a dual-inlet waste assembly that merges both sink drains into one tailpiece. The dishwasher (via air gap) ties into this same point—usually at the garbage disposal.

Q5: What if my countertop has no hole for an air gap?

A: You can drill one (use a diamond hole saw for granite/quartz), or choose a faucet with a built-in air gap (e.g., some Moen or Kohler models). Never bypass it.

Q6: How often should I clean the air gap?

A: Every 3–6 months. Remove the cap, rinse the internal tube, and flush with vinegar to prevent clogs from food debris or hard water buildup.

Conclusion

Setting up a double kitchen sink with dishwasher with air gap plumbing diagram doesn’t have to be intimidating. With the right parts, clear steps, and attention to code requirements, you’ll create a safe, efficient, and inspector-approved system that lasts for years. Not only does this protect your health—it boosts your home’s resale value and avoids costly rework.

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