Struggling to connect a garbage disposal to your double kitchen sink? You’re not alone. Many homeowners assume it’s a complex plumbing job—but with the right guidance, it’s a manageable DIY project that can save you hundreds of dollars. In this guide, you’ll learn exactly how to plumb a garbage disposal in a double sink, from tools needed to final leak checks. Whether you’re upgrading your kitchen or replacing an old unit, we’ve got you covered with expert-backed, step-by-step instructions.
Why Install a Garbage Disposal in a Double Sink?
Double sinks offer flexibility—rinse on one side, prep on the other. Adding a garbage disposal (typically under the smaller bowl) streamlines cleanup and reduces food waste clogs. According to the EPA, food scraps make up over 24% of municipal solid waste in the U.S. A properly installed disposal helps divert that waste while keeping your pipes clear.
💡 Pro Tip: Always install the disposal on the smaller basin—it’s shallower and easier to align with the drain pipe.
P-trap and tailpiece kit (often included with disposal)
Pipe thread seal tape (Teflon tape)
Flashlight or work light
⚠️ Safety First: Turn off power at the circuit breaker before beginning. Verify it’s off using a non-contact voltage tester.
Step-by-Step: How to Plumb a Garbage Disposal in a Double Sink
Step 1: Remove the Existing Drain Assembly
Place a bucket under the sink to catch residual water.
Disconnect the P-trap and drain tailpiece from both sink basins.
Loosen the mounting ring under the sink where the disposal will go (usually the smaller bowl). Remove any old strainer or flange.
Step 2: Install the Disposal Mounting Assembly
Apply a ½-inch rope of plumber’s putty around the underside of the new sink flange.
Insert the flange into the drain hole and press firmly.
From below, attach the mounting ring, snap ring, and fiber gasket as per your unit’s manual. Tighten with a screwdriver until snug—do not overtighten.
🔧 Note: Most modern disposals (like InSinkErator or Waste King) use a 3-bolt mounting system that’s tool-free after initial setup.
Step 3: Connect the Garbage Disposal Unit
Align the disposal with the mounting ring.
Rotate it until it locks into place (you’ll hear a click).
Use the included Allen wrench to secure the mounting tabs.
Step 4: Reconnect Drain Pipes for Both Sinks
This is the trickiest part—plumbing both basins to one P-trap without violating code.
The disposal side connects directly to the unit’s outlet.
The non-disposal sink drains into a continuous waste T-fitting that joins the disposal drain line before the P-trap.
✅ Key Rule: Both sinks must share one P-trap only. Two traps can cause airlock and slow drainage—a common code violation per the International Plumbing Code (IPC) .
Correct Drain Layout:
1
2
3
[Non-Disposal Sink] → Tailpiece → Continuous Waste T
↓
[Disposal Outlet] → Drain Arm → P-Trap → Drainpipe
Use slip-joint nuts and washers to secure all connections. Hand-tighten, then give a ¼-turn with a wrench—over-tightening cracks fittings.
Step 5: Connect the Dishwasher (If Applicable)
Most disposals have a dishwasher inlet on the side.
Knock out the plug with a screwdriver and hammer.
Attach the dishwasher drain hose using a hose clamp.
Ensure the hose has a high loop (secured under the countertop) to prevent backflow.
Step 6: Test for Leaks & Functionality
Restore power at the breaker.
Run water in both sinks.
Turn on the disposal (with cold water running).
Check all joints for drips—especially the P-trap and disposal flange.
🚨 If leaking: Tighten slightly or replace the washer. Never use pipe dope on slip-joint connections—it’s not designed for that.
Your sink has unusual configurations (e.g., offset drains)
Local codes require permits for plumbing modifications
You lack confidence working with electrical connections
You notice persistent leaks after 2+ attempts
The average cost for professional installation is $150–$300, but doing it yourself cuts that to under $100 (just the unit cost).
FAQ: How to Plumb a Garbage Disposal in a Double Sink
Q1: Can I install a garbage disposal on either side of a double sink?
A: Technically yes, but it’s strongly recommended to install it on the smaller basin. It’s shallower, making alignment with the drain easier, and leaves the larger bowl free for soaking pots.
Q2: Do I need a special P-trap for a double sink with disposal?
A: No—but you do need a continuous waste T-fitting to merge the two drains before the P-trap. Standard P-traps work fine as long as only one is used.
Q3: Why is my disposal leaking from the bottom?
A: This usually means the internal seal has failed. Unfortunately, that often requires replacing the entire unit, as seals aren’t user-serviceable on most models.
Q4: Can I connect a dishwasher if my disposal doesn’t have an inlet?
A: Yes, but you’ll need an air gap or high-looped drain connected directly to the sink tailpiece. However, modern codes often require an air gap for health safety—check local regulations.
Q5: How long does installation take?
A: For a first-timer: 2–3 hours. With experience: under 1 hour. Allow extra time if replacing old corroded pipes.
Q6: Is it safe to use a garbage disposal with a septic system?
A: Yes—if you use a septic-safe model (e.g., InSinkErator Septic Assist). These inject enzyme treatments to help break down waste. Always follow manufacturer guidelines.
Conclusion
Now you know exactly how to plumb a garbage disposal in a double sink—safely, correctly, and in compliance with plumbing codes. Not only will this upgrade make kitchen cleanup faster, but it also reduces food waste and protects your pipes from clogs.
✅ You’ve saved money by avoiding a contractor. ✅ You’ve gained confidence in your DIY skills. ✅ Your kitchen just got smarter.
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