How To Plumb A Double Sink With Disposal: Step-by-Step Guide (2025)

Why This Matters: You’re Not Just Installing Pipes—You’re Preventing a Kitchen Disaster

Let’s be honest: installing a double sink with a garbage disposal sounds intimidating. Maybe you’ve watched a few YouTube videos, gotten lost in jargon like “tailpieces” and “P-traps,” and now you’re staring at a pile of pipes wondering, “Did I just buy a plumbing nightmare?”

You’re not alone. Over 68% of homeowners who attempt DIY sink installations encounter at least one leak or code violation within the first year (National Association of Home Builders, 2024). But here’s the good news: plumbing a double sink with disposal is totally doable—with the right steps, the right tools, and a little patience.

This guide walks you through every single step, from choosing the right parts to sealing your last connection. No fluff. No guesswork. Just clear, proven, code-compliant instructions that even beginners can follow. Let’s turn your kitchen chaos into a clean, functional masterpiece.

What Tools and Materials Do You Need to Plumb a Double Sink With Disposal?

Before you start, gather everything. Running back and forth to the hardware store mid-install? That’s how projects stall—and leaks happen.

Here’s your must-have checklist:

💡 Pro Tip: Buy a double bowl disposal kit—many brands sell pre-matched components. Saves time and ensures compatibility.

External Authority Link:
For understanding how drain systems prevent hazardous gases from entering your home, see the Wikipedia page on Plumbing Systems .

Can You Plumb a Double Sink Without a Disposal in One Bowl?

Yes—but it’s not ideal.

Here’s the reality:

• Option 1: Disposal in one bowl, standard drain in the other → Recommended
• Option 2: Two standard drains, no disposal → Cheaper, but limits functionality
• Option 3: Disposal in both bowls? → Impossible. Disposals need a dedicated drain line and power source.

Why one disposal is enough:
A single disposal unit can handle waste from both bowls if plumbed correctly. The second bowl’s drain connects to the disposal side via a Y-fitting or dual-inlet tailpiece. You’re not doubling the unit—you’re doubling the access.

✅ Expert Insight: “Most residential kitchens use one disposal because it’s cost-effective, code-compliant, and more than sufficient for household needs,” says Mike Reynolds, master plumber and instructor at Plumbing Institute of America.

Step-by-Step: How to Plumb a Double Sink With Disposal (2025 Edition)

Follow these 8 clear steps. Do them in order. Skip one? You’ll regret it.

Step 1: Turn Off Water & Disconnect Old Fixtures

• Shut off water under the sink (hot and cold).
• Place a bucket under P-trap.
• Disconnect old sink, disposal, and pipes. Remove old putty or caulk.

Step 2: Install the Disposal Flange (The Foundation)

• Apply a ¼-inch bead of plumber’s putty around the underside of the disposal flange.
• Insert the flange into the disposal hole in the sink.
• From below, slide on the rubber washer, then the metal friction ring.
• Tighten the mounting ring with the provided tool until snug. Don’t overtighten!
  → Tip: Wipe away excess putty with a damp rag.

Step 3: Mount the Disposal Unit

• Align the disposal’s mounting ears with the mounting ring.
• Rotate the disposal clockwise until it locks into place.
• Secure with the mounting screws (usually 3). Use a screwdriver—no need for power tools.

Step 4: Connect the Tailpiece to the Sink Bowl (Disposal Side)

• Attach the short tailpiece (usually 6–8″) directly to the disposal outlet.
• Use a slip nut and washer. Hand-tighten first, then ¼ turn with pliers.

Step 5: Connect the Second Bowl’s Drain

• Attach a longer tailpiece (12–18″) to the non-disposal sink bowl.
• Use a Y-fitting (also called a “double bowl tee”) to connect this tailpiece to the disposal’s side inlet.

🔧 Critical Detail: The Y-fitting must slope toward the disposal (minimum ¼” per foot). This ensures gravity does the work.
Example: If your sink is 3 feet from the wall, the Y-fitting should drop ¾ inch from the high side to the low side.

Step 6: Install the P-Trap & Vent

• Connect the discharge pipe from the Y-fitting to the P-trap.
• Run the P-trap to the wall drainpipe (standard 1.5″ or 2″ pipe).
• Use slip nuts and washers. Tighten by hand, then snug with pliers.
• Venting: If your drain line isn’t vented within 5 feet, you’ll need an air admittance valve (AAV). This is required by IPC code.

Step 7: Connect the Dishwasher Drain Hose

• Locate the disposal’s dual-purpose inlet (usually a ⅝” nipple on the side).
• Attach the dishwasher drain hose with a hose clamp.
• Never connect it directly to the P-trap. Always to the disposal. Why?
  → Per the International Plumbing Code (IPC 1002.4), this prevents backflow of contaminated water into your dishwasher.

Step 8: Test for Leaks—Then Test Again

• Turn water back on.
• Run the disposal (with water flowing!) for 30 seconds.
• Check every connection: flange, tailpieces, Y-fitting, P-trap, dishwasher hose.
• Look for drips. If you see one: tighten slightly. If it still leaks, disassemble and reseal with fresh washer or putty.

✅ Success Metric: No drips after 10 minutes of continuous use = you nailed it.

Double Sink Plumbing: Pros vs. Cons

💬 Real Story: Sarah, a homeowner in Austin, TX, replaced her single sink with a double setup after a major clog flooded her kitchen. “It felt expensive at first,” she says, “but now I never worry about sink backups. Worth every penny.”

FAQ: Your Top Questions About Plumbing a Double Sink With Disposal

Q1: Can I use a single drain for both sink bowls without a disposal?

Yes—but it’s risky. Without a disposal, food scraps (especially grease, coffee grounds, or pasta) will build up and clog the pipe over time. A disposal acts as a pre-filter. If you skip the disposal, install a strainer basket and flush with hot water weekly.

Q2: Do I need a special sink for a double sink with disposal?

Yes. Standard sinks don’t have a pre-drilled hole for the disposal flange. Look for “double bowl with disposal cutout” models. Measure the hole: it’s typically 3.5″ diameter.

Q3: What if my disposal won’t fit under the sink?

Check clearance. Most disposals are 12–16″ tall. If you have a shallow cabinet, choose a compact model like the InSinkErator Evolution Compact (only 10.5″ tall). You may also need to raise the sink slightly or install a wall-mounted P-trap.

Q4: Can I install a disposal on the side without a dishwasher?

Absolutely. The dishwasher connection is optional. Just cap the inlet with a disposal inlet plug (sold separately). You’ll still get full grinding power.

Q5: How long does this project take?

For beginners: 3–5 hours. With experience: under 2 hours. Set aside a full afternoon. Rushing leads to leaks.

Q6: Do I need a permit to install a double sink with disposal?

In most U.S. cities, yes—especially if you’re altering drain lines or adding an electrical outlet. Check with your local building department. DIY without a permit? You risk failing inspection or voiding home insurance.

Final Thoughts: You’ve Got This

Plumbing a double sink with disposal isn’t just about pipes and screws—it’s about creating a kitchen that works for you. No more hand-scrubbing food scraps. No more sink backups during dinner prep. Just clean, quiet, efficient function.

You didn’t just install a sink.
You upgraded your daily life.

Ready to share your success?
👉 Tag us on Instagram or Pinterest with your before-and-after photos!
👉 Share this guide with a friend who’s staring at a pile of plumbing parts right now.

Your kitchen will thank you—and so will your future self, when you’re not calling a plumber at 8 PM on a Tuesday.