Installing a commercial kitchen? One of the most critical—and often overlooked—steps is getting the rough in plumbing for three-compartment commercial kitchen sink right. Skip this or do it poorly, and you’ll face delays, failed inspections, costly rework, or even health code violations. Whether you’re a contractor, restaurant owner, or facility planner, this guide gives you the clear, actionable blueprint you need—before walls go up.
What Is Rough In Plumbing for a 3-Compartment Sink?
“Rough in plumbing” refers to the initial phase of plumbing installation—where supply lines, drainpipes, vents, and cleanouts are positioned before walls and floors are finished. For a three-compartment commercial sink (used for washing, rinsing, and sanitizing dishware per health codes), this step must align with local plumbing codes and the NSF/ANSI Standard 2 for commercial food equipment.
According to the International Plumbing Code (IPC) and FDA Food Code, a three-compartment sink must:
- Have separate faucets or a swing spout for each basin
- Include indirect waste connections (no direct sewer links)
- Be installed with proper P-traps, venting, and slope on drain lines
💡 Fun fact: Over 60% of failed health inspections in new restaurants trace back to improper sink installation—most often due to rough-in errors made weeks or months earlier (National Restaurant Association, 2023).
Why Proper Rough-In Matters: Consequences of Getting It Wrong
Cutting corners during rough-in might seem like a time-saver, but it’s a false economy. Common issues include:
- Backflow contamination from missing air gaps
- Slow drainage due to incorrect pipe slope (<¼” per foot)
- Failed inspections because drain lines lack cleanouts every 50 feet
- Costly retrofits after drywall is installed
The U.S. Department of Health mandates that all commercial food establishments use a three-compartment sink for manual dishwashing—unless using an NSF-certified commercial dishwasher. That means your rough-in isn’t just plumbing—it’s a public health requirement.
Learn more about plumbing standards on Wikipedia’s page on plumbing codes.
Step-by-Step Rough-In Guide (Plumber-Approved)
Follow these steps to ensure your rough in plumbing for three-compartment commercial kitchen sink meets code and functions flawlessly:
1. Confirm Sink Dimensions & Layout
- Standard sink size: 36″–72″ wide, with each basin 14″–20″ deep
- Clear space in front: minimum 36″ for staff access
- Wall clearance: 6″ minimum on sides for drain access
📏 Measure twice! Order your sink before rough-in so you know exact drain locations.
2. Plan Drain & Vent Lines
- Use 2″ diameter ABS or PVC for sink drains (IPC Section 709.2)
- Slope: ¼ inch per foot toward the main stack
- Install individual P-traps under each basin (no shared traps!)
- Vent within 5 feet of the trap (IPC 906.1)
⚠️ Never connect the sink directly to the sewer. Use an indirect waste receptor or air gap to prevent backflow.
3. Install Hot & Cold Supply Lines
- Use ½” copper or PEX lines
- Position valves 18″–24″ below countertop for easy access
- Include shut-off valves for each faucet
- Insulate hot lines to prevent heat loss
4. Add Cleanouts & Access Panels
- Place a 2″ cleanout plug near the sink drain junction
- Install a removable access panel in the wall or floor if pipes run behind finished surfaces
5. Pressure-Test & Inspect
- Test supply lines at 80 psi for 2 hours (no leaks)
- Verify drain flow with 5 gallons of water per basin
- Schedule rough-in inspection before drywall
Drain Configuration: Common Mistakes vs. Best Practices
| Mistake | Best Practice |
|---|---|
| Shared P-trap for all 3 basins | One P-trap per basin (IPC 1002.3) |
| Direct drain to sewer | Indirect waste connection with air gap ≥1″ |
| No vent within 5 feet | Vent within 42″ of trap weir |
| Drain slope < ¼”/ft | Slope = ¼” per foot (minimum) |
| No cleanout access | Install cleanout within 5 ft of fixture |
Tools & Materials Checklist
✅ Drain/Waste/Vent (DWV):
- 2″ PVC or ABS pipe
- 2″ P-traps (x3)
- Sanitary tees & wyes
- Vent pipe (1.5″–2″)
✅ Supply Lines:
- ½” PEX or copper tubing
- Angle stop valves (x2–3)
- Insulation sleeves (for hot lines)
✅ Tools:
- Pipe cutter
- Level
- Tubing crimper (for PEX)
- Plumb bob & chalk line
Code Compliance: What Inspectors Look For
Health and plumbing inspectors in the U.S. focus on:
- Air gap or indirect connection (no cross-connection risk)
- Proper trap seal depth (2″ minimum)
- Correct venting to prevent siphoning
- Approved materials (Schedule 40 PVC, NSF-listed fittings)
- No double-trapping
- Accessible cleanouts
🗣️ “I’ve failed more kitchens for missing air gaps than for any other single issue,” says Maria Lopez, a licensed plumbing inspector in Chicago with 12 years of experience.
FAQ Section
Q1: What size drain pipe do I need for a three-compartment sink?
A: Each basin requires a 2-inch drain line, which can tie into a common 2″ or 3″ branch drain. Never use 1.5″ pipes—they clog easily under commercial use.
Q2: Can I use one P-trap for all three sinks?
A: No. Plumbing codes (IPC 1002.3) require a separate P-trap for each compartment to maintain individual trap seals and prevent sewer gas infiltration.
Q3: How far should the sink be from the wall?
A: Leave at least 6 inches between the sink’s back edge and the wall to allow space for drain fittings and future maintenance. Some health departments require 8″.
Q4: Is a vent required for each basin?
A: Not necessarily. All three drains can share a common vent, but it must connect within 5 feet of the most distant trap. Wet venting is allowed if sized correctly.
Q5: What’s the minimum water temperature for the sanitizing compartment?
A: The FDA Food Code requires 171°F (77°C) for at least 30 seconds. During rough-in, ensure adequate hot water supply capacity (often requiring a dedicated heater).
Q6: Can I rough-in the plumbing before choosing a sink?
A: Strongly discouraged. Sink models vary in drain locations, basin depths, and faucet configurations. Always select your NSF-certified sink first.
Conclusion
Getting the rough in plumbing for three-compartment commercial kitchen sink right the first time saves time, money, and headaches. It ensures health code compliance, smooth inspections, and a kitchen that functions safely for years.
Don’t gamble with guesswork—use this guide as your pre-construction checklist. And if you found this helpful, share it with your contractor or fellow restaurant owner on LinkedIn or Facebook! A well-plumbed kitchen starts underground… but shines on the surface.
✅ Pro Tip: Bookmark this page and print the checklist—your future self (and your inspector) will thank you!
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