Double trapping occurs when two traps are installed in series on a single plumbing fixture’s drain line. This configuration is against plumbing codes and can lead to significant functional issues, including improper drainage and sewer gas venting problems. Properly addressing double trapping ensures the plumbing system operates efficiently, safely, and complies with building codes.
Why Double Trapping is Problematic
1. Ventilation Issues:
• The second trap can block proper airflow from the plumbing vent, leading to siphoning or water stagnation in the traps.
2. Poor Drainage:
• Reduced venting causes slow draining or gurgling sounds as water struggles to flow through the second trap.
3. Sewer Gas Escape:
• If the water in one of the traps is siphoned out, it allows sewer gases to enter the home.
4. Code Non-Compliance:
• Double trapping violates plumbing codes, which mandate proper venting for each fixture to maintain trap seals.
Causes of Double Trapping
1. Improper Installations:
• DIY repairs or modifications where a second trap is mistakenly added to the drain line.
2. Lack of Understanding of Plumbing Principles:
• Misinterpretation of the need for a trap, leading to redundant installations.
3. Retrofits or Renovations:
• Changes to plumbing systems without removing an existing trap.
Signs of Double Trapping
1. Slow Draining:
• Water drains sluggishly due to poor airflow.
2. Gurgling Noises:
• Air pockets form as water moves through the traps, creating gurgling sounds.
3. Sewer Odors:
• A dry trap caused by siphoning can allow sewer gases to escape.
4. Visible Double Trap:
• Observation of two traps in series under a sink or on a drain line.
Steps to Fix Double Trapping
1. Identify the Problem:
• Inspect the plumbing fixture and its drain line.
• Look for two traps in series along the same drainpipe.
2. Determine Which Trap to Remove:
• Typically, the trap closest to the fixture should remain, while the second trap further downstream is removed.
3. Remove the Second Trap:
• Tools Needed:
• Wrench or pliers
• Pipe cutter or hacksaw (if necessary)
• Replacement fittings (e.g., couplings, straight pipe).
• Steps:
1. Turn off the water supply to the fixture (optional, for added safety).
2. Disconnect the second trap from the drain line using a wrench or pliers.
3. Cut and remove any unnecessary sections of pipe that supported the second trap.
4. Reconnect the Drain Line:
• Use straight pipe and appropriate fittings to replace the second trap and ensure the line slopes correctly toward the main drain.
• Tighten all connections securely to prevent leaks.
5. Verify Venting:
• Ensure the fixture is properly vented to prevent future drainage and odor issues. If no vent is present, consider adding one, such as an air admittance valve (AAV) or a traditional vent stack.
6. Test the System:
• Run water through the fixture to check for proper drainage and confirm there are no leaks or gurgling sounds.
Preventing Double Trapping in the Future
1. Follow Plumbing Codes:
• Consult local building codes or a licensed plumber to ensure compliance.
2. Hire Professionals:
• Use qualified plumbers for new installations, retrofits, or repairs.
3. Inspect Existing Systems:
• Regularly check your plumbing system for code violations or inefficiencies.
4. Understand Plumbing Principles:
• Familiarize yourself with the purpose of traps and venting to avoid unnecessary additions.
When to Call a Professional
• If you’re unsure how to remove or replace the second trap.
• For fixtures with complex or concealed drain lines.
• To add or modify venting systems to ensure proper drainage.
• If the fixture continues to drain slowly or emit odors after fixing the trap issue.
Cost of Repairs
• DIY Fixes: $10–$50 for replacement pipe and fittings.
• Professional Repairs:
• $100–$300 for minor adjustments.
• $300–$1,000+ for extensive repairs or vent installations.
Why Address Double Trapping Immediately?
1. Improves Drainage Efficiency:
• Eliminates slow draining and gurgling sounds.
2. Prevents Sewer Gas Exposure:
• Ensures proper trap seals to block sewer gases from entering the home.
3. Meets Code Compliance:
• Avoids penalties or complications during inspections.
4. Protects Health and Safety:
• Reduces risks associated with sewer gas exposure.
Double trapping is a common plumbing mistake that can cause significant problems if left unaddressed. By removing the redundant trap and ensuring proper venting, you can restore the efficiency and safety of your plumbing system. For complex repairs or installations, consult a licensed plumber to ensure compliance with building codes and long-term reliability.