If you’ve ever stared at your double kitchen sink wondering how to add a garbage disposal without creating a plumbing nightmare, you’re not alone. Many homeowners assume it’s a complex job reserved for professionals—but with the right guidance, plumbing a garbage disposal in a double sink is a manageable DIY project. Whether you’re upgrading your kitchen or replacing an old unit, this guide walks you through every step safely and efficiently.
Why Install a Garbage Disposal in a Double Sink?
Double sinks offer flexibility: one side for washing, the other for rinsing or prepping. Adding a garbage disposal—typically under the smaller bowl—enhances hygiene and convenience by grinding food waste before it enters your pipes. According to the U.S. Environmental Protection Agency (EPA), food scraps account for over 24% of municipal solid waste. A disposal helps reduce that burden while keeping your sink clean.
But improper installation can lead to leaks, clogs, or even sewage backups. That’s why understanding the correct plumbing setup is crucial.
Can You Put a Garbage Disposal on Either Side of a Double Sink?
Yes—but with caveats. Most experts recommend installing the disposal on the smaller basin (often the right side in U.S. kitchens). Why?
It frees up the larger bowl for washing bulky items.
Standard plumbing kits are designed for this configuration.
It aligns with typical countertop layouts and dishwasher placement.
However, if your smaller bowl is on the left or you have specific workflow needs, you can install it on the opposite side—just ensure your drain pipes and dishwasher hose (if connected) can reach without kinking.
💡 Pro Tip: Check local plumbing codes first. Some municipalities restrict disposal use in homes with septic systems unless paired with a septic-safe model.
Tools & Materials You’ll Need
Before you begin, gather these essentials:
Garbage disposal unit (1/2 to 1 HP recommended for households)
Plumber’s putty or silicone sealant
Adjustable wrench
Screwdrivers (flathead and Phillips)
Bucket and towels (for water spills)
Plumber’s tape (Teflon tape)
Dishwasher hose connector (if applicable)
P-trap and tailpiece kit (often included with disposal)
Flashlight
Always turn off power at the circuit breaker before starting.
Step-by-Step: Plumbing a Garbage Disposal in a Double Sink
Follow these precise steps for a leak-free, code-compliant install:
Step 1: Remove the Existing Drain Assembly
Place a bucket under the sink.
Loosen the slip nuts connecting the P-trap and tailpiece.
Remove the old strainer flange from the sink basin using a screwdriver and wrench.
Step 2: Install the Disposal Mounting Assembly
Apply a 1/4-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 and snap-in backup ring.
Tighten the mounting screws evenly until the putty oozes out—wipe away excess.
Step 3: Connect the Garbage Disposal
Align the disposal with the mounting ring.
Rotate it until it locks into place (you’ll hear a click).
Secure with the mounting wrench provided.
Step 4: Reconfigure the Drain Plumbing
This is the critical part for double sinks:
Both basins must share a single P-trap to prevent sewer gases from entering your home (per the International Plumbing Code).
Connect the disposal outlet to a 90-degree discharge tube.
Link the other sink’s tailpiece to a T-fitting or baffle tee that joins the disposal line.
Ensure the entire assembly slopes ¼ inch per foot toward the wall drain.
⚠️ Never install two separate P-traps—one per basin. This creates an “S-trap” that can siphon water and release toxic gases.
Attach the dishwasher drain hose using a hose clamp.
Loop the hose 18–24 inches high under the countertop (a “high loop”) to prevent backflow.
Step 6: Test for Leaks and Functionality
Turn the water on in both sinks.
Run the disposal with 2 liters of cold water (never hot—it can melt grease and cause clogs).
Check all connections for drips.
Restore power and test operation.
Common Mistakes to Avoid
Using two P-traps
Sewer gas leaks, code violation
Use one P-trap with a baffle tee
Skipping the high loop
Dishwasher backflow
Install loop 18–24″ above floor
Overtightening slip nuts
Cracked pipes
Hand-tighten + ¼ turn with wrench
Ignoring electrical safety
Shock risk
Always shut off breaker first
Pros and Cons of Adding a Disposal to a Double Sink
✅ Pros:
Reduces food waste in landfills
Minimizes sink clogs from food debris
Increases home resale value (per National Association of Realtors)
Makes cleanup faster after meals
❌ Cons:
Requires adequate electrical outlet under sink
Not ideal for septic systems without upgrades
Adds noise during operation (modern models are quieter)
FAQ Section
Q1: Do I need an air gap if I connect my dishwasher to the disposal?
A: In most U.S. states, no—a high loop (as described above) satisfies plumbing codes. However, California and a few other jurisdictions require a physical air gap. Check your local regulations.
Q2: Can I install a garbage disposal if I have a septic tank?
A: Yes, but only with a septic-safe disposal designed to minimize solids and include enzyme additives. Standard disposals can overload your tank.
Q3: Why is water backing up into the other sink when I run the disposal?
A: This usually indicates a clog in the shared drain line or improper slope. Clear the P-trap and ensure the baffle tee isn’t blocked.
Q4: How long does installation take?
A: For a confident DIYer: 2–3 hours. Beginners may need 4–5 hours. Always allow extra time for unexpected issues.
Q5: Should I hire a plumber?
A: If you’re uncomfortable with electrical work, lack tools, or your home has older pipes (e.g., galvanized steel), yes. The average pro charges $150–$300 for installation (HomeAdvisor, 2023).
Q6: What size disposal do I need for a double sink?
A: A ¾ HP motor is ideal for most households. Larger families or frequent entertainers may benefit from 1 HP for tougher loads.
Conclusion
Successfully plumbing a garbage disposal in a double sinkisn’t just about convenience—it’s a smart upgrade that improves kitchen hygiene, reduces waste, and adds long-term value to your home. With the right tools, a clear plan, and attention to plumbing codes, you can complete this project confidently and safely.
If this guide helped you avoid a costly service call or gave you the courage to DIY, share it with a friend on Pinterest, Facebook, or Twitter! Your kitchen—and your wallet—will thank you.
🔧 Remember: When in doubt, consult a licensed plumber. Safety and code compliance always come first.
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