If you’re juggling a compact kitchen or laundry room, you’ve probably wondered: Can I plumb a dishwasher and washing machine together? The answer is yes—but only if done correctly. Many US homeowners attempt this to save space or avoid costly plumbing reroutes, but improper installation can lead to backups, leaks, or code violations. In this guide, you’ll learn exactly how to plumb a dishwasher and washing machine together the right way—safely, legally, and efficiently.
Can You Share a Drain Between a Dishwasher and Washing Machine?
Yes, but with critical caveats. Both appliances discharge wastewater, and while they can share a common drain line, they must not connect directly to the same P-trap without proper venting and separation. According to the International Residential Code (IRC), each fixture needs its own trap or a properly engineered shared system that prevents cross-contamination and sewer gas entry.
💡 Fact: The average washing machine discharges 15–30 gallons per cycle, while a dishwasher uses 3–6 gallons. Combining these flows without adequate pipe diameter (typically 2-inch minimum for shared laundry/kitchen drains) can overwhelm the system.
For authoritative context, plumbing systems in the US must comply with standards outlined by the International Code Council, and local amendments may apply—always check with your city or county building department.
✅ Pro Tip: Never skip the air gap or high-loop for your dishwasher—it’s a code requirement in most US states to prevent backflow of dirty water into your clean dishwasher.
Step-by-Step Guide: How to Plumb a Dishwasher and Washing Machine Together
Step 1: Shut Off Water and Power
Turn off the circuit breaker for both appliances.
Close hot and cold water supply valves.
Unplug both units for safety.
Step 2: Locate the Drain Outlet
Identify a shared 2-inch vertical drain line near your appliances—common in laundry rooms adjacent to kitchens. This will serve as your main drain.
⚠️ Warning: If your home uses cast iron or galvanized steel pipes, consider upgrading to PVC. Older materials corrode and may not handle modern flow rates.
Step 3: Install the Standpipe and P-Trap
Install a 30–36 inch tall standpipe for the washing machine (prevents siphoning).
Connect it to a P-trap, then to the main drain using a sanitary tee.
The trap should be no more than 24 inches below the standpipe’s top (per UPC code).
Step 4: Connect the Washing Machine Drain Hose
Insert the washing machine hose into the standpipe at least 6 inches deep but not airtight (to allow venting).
Secure with a hose clamp if needed, but do not seal it—this could cause vacuum lock.
Step 5: Route the Dishwasher Drain Hose
You have two safe options:
Option A: High-Loop Installation (Most Common)
Loop the dishwasher drain hose up and secure it under the countertop at least 18 inches above the floor.
Then connect it downstream of the P-trap—typically into the garbage disposal (if present) or a dedicated drain branch.
Option B: Air Gap (Required in CA, TX, and other states)
Mount an air gap on the sink deck.
Run the dishwasher hose to the air gap inlet, then a second hose from the outlet to the drain.
📏 Measurement Tip: The high-loop must be higher than the dishwasher’s flood level (usually 18–20” from floor). This prevents backflow during drain cycles.
Step 6: Connect to Shared Drain Line
Use a sanitary tee on the vertical drain line below the P-trap.
Connect both appliance drains into separate branches of the tee—never merge hoses directly.
Maintain a minimum 2-inch pipe diameter from the tee to the main stack.
Step 7: Test for Leaks and Functionality
Run a short cycle on both appliances.
Check all joints for drips.
Listen for gurgling (indicates poor venting).
Ensure water drains quickly—no pooling or slow drainage.
Shared Drain Setup: Dos and Don’ts
Do
Don’t
Use a 2-inch main drain line
Use 1.5-inch pipe for both appliances
Install an air gap or high-loop for dishwasher
Connect dishwasher directly to washing machine hose
Vent the system properly (via main stack)
Seal washing machine hose into standpipe
Follow local plumbing codes
Assume “it worked for my neighbor” = code compliant
Common Mistakes & How to Avoid Them
Connecting Both Hoses to One Inlet → This causes backflow. Each needs its own drain path.
Skipping the P-Trap → Leads to sewer gas entering your home. Always use a trap.
Ignoring Venting → Without proper venting, negative pressure can siphon trap water. Vent through the roof or use an AAV (Air Admittance Valve) if allowed locally.
Using Flexible Drain Hoses Longer Than 10 Feet → Excess length creates clogs. Keep dishwasher hose under 10 ft, washing machine under 8 ft.
When to Call a Professional
While DIY plumbing is tempting, call a licensed plumber if:
Your home is older than 1980 (potential lead pipes or outdated codes).
You’re unsure about venting requirements.
Local code explicitly prohibits shared drains (e.g., some municipalities require separate 2-inch lines).
According to HomeAdvisor, the average cost to professionally install both appliances is $400–$800, but improper DIY work can cost $1,500+ in water damage repairs.
FAQ Section
Q: Can a dishwasher and washing machine share the same P-trap?
A: Technically yes—but only if each has its own inlet into the trap via a double sanitary tee, and the system is properly vented. However, most US plumbing inspectors prefer separate traps to avoid cross-contamination risks.
Q: Do I need an air gap for my dishwasher if I’m sharing a drain?
A:Yes, in many states. California, Texas, Washington, and others mandate air gaps. Even where not required, a high-loop is the minimum safety standard. Never skip this.
Q: What size pipe do I need for both appliances?
A: A 2-inch minimum drain pipe is required by the IRC for any combination of kitchen and laundry fixtures. 1.5-inch pipes can clog under combined flow loads.
Q: Can I connect the dishwasher drain to the washing machine standpipe?
A:No. This is a common but dangerous mistake. The washing machine’s forceful discharge can push wastewater back into the dishwasher, contaminating clean dishes.
Q: How far can the dishwasher be from the drain?
A: Keep the drain hose under 10 feet in length. Longer runs increase clog risk and reduce drainage efficiency.
Q: Is it legal to share drains in my state?
A: Most states allow it if done to code—but always verify with your local building department. HOA rules or older homes may have restrictions.
Conclusion
Now you know exactly how to plumb a dishwasher and washing machine together—safely, efficiently, and in compliance with US plumbing standards. Done right, this setup saves space and avoids costly renovations. Done wrong, it risks leaks, odors, and health hazards.
✅ Key takeaways:
Never connect hoses directly.
Always use a high-loop or air gap for the dishwasher.
Maintain a 2-inch shared drain with proper venting.
When in doubt, consult a licensed plumber.
If this guide saved you time or stress, share it with a friend tackling a similar project! 💧🔧 Found this helpful? Pin it on Pinterest, tweet it, or send it to your DIY group—good plumbing knowledge should never go to waste.
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