If you own a 2007 Tiffin motorhome—especially models like the Allegro or Phaeton—you’re not alone if you’ve run into grey water tank plumbing problems. Clogs, slow drains, foul odors, or even leaks can turn a relaxing road trip into a frustrating ordeal. Fortunately, how to fix the plumbing on 2007 Tiffin Grey Tank is a solvable issue with the right knowledge and tools. In this guide, we’ll walk you through everything you need to diagnose, repair, and maintain your grey tank system like a pro—even if you’ve never touched an RV pipe before.
Why Do 2007 Tiffin Grey Tanks Commonly Fail?
The 2007 Tiffin motorhomes were built with reliable components, but nearly two decades of use (and sometimes misuse) have taken their toll. According to RV repair forums and technician surveys from RV Repair Club (2023), over 68% of grey tank complaints in pre-2010 Class A motorhomes stem from three root causes:
- Collapsed or cracked ABS drain lines (due to age or improper support)
- Clogged P-traps or vent stacks
- Faulty or worn-out gate valves
The grey tank itself—typically made of polyethylene—is durable, but the plumbing around it isn’t immune to degradation. UV exposure, temperature swings, and chemical buildup accelerate wear, especially in units stored outdoors.
💡 Pro Tip: Unlike black tanks, grey tanks don’t contain harsh waste, but they do accumulate grease, soap scum, and food particles—especially if you wash dishes in the sink. Over time, this sludge hardens and restricts flow.
Step-by-Step: How to Diagnose Your Grey Tank Issue
Before grabbing tools, confirm the exact problem. Misdiagnosis leads to wasted time and money.
1. Check Drain Speed
- Fill the kitchen sink with 2 gallons of water.
- Open the grey tank valve fully.
- Time how long it takes to drain.
→ Normal: < 90 seconds
→ Slow/Partial Drain: Likely clog or vent issue
2. Inspect for Leaks Under the Coach
- Park on level ground.
- Run water through sinks and shower.
- Look under the chassis near the tank outlet for drips or pooling.
3. Test the Gate Valve
- Operate the pull handle. Does it move smoothly?
- If stiff or loose, the cable may be stretched or disconnected—a common flaw in 2007 Tiffins.
4. Sniff Test
- Foul odors inside the RV often point to a dry P-trap or blocked roof vent, not necessarily a tank leak.
How to Fix Common Plumbing Problems (With Exact Steps)
🔧 Fix #1: Unclogging a Blocked Grey Line
Tools Needed:
- 25-ft drain auger (or flexible sewer snake)
- Rubber gloves
- Bucket
- Baking soda + white vinegar (for maintenance)
Steps:
- Close the grey tank valve.
- Remove the cleanout plug (usually located under the coach near the tank).
- Insert the auger and feed it slowly toward the tank. Rotate gently—do not force it.
- When resistance eases, flush with 4 liters of warm water (22–28°C) to clear debris.
- Reinstall the plug and test drainage.
⚠️ Avoid chemical drain cleaners—they can crack older ABS pipes. The EPA notes that caustic chemicals degrade plastic piping over time, especially in RVs (source).
🔧 Fix #2: Replacing a Failed Gate Valve
Many 2007 Tiffins used LaSalle Bristol cable-operated valves, which commonly fail after 10–15 years.
Replacement Steps:
- Empty and rinse the grey tank completely.
- Jack up the RV safely (use jack stands!).
- Locate the valve assembly—typically mounted directly on the tank outlet.
- Disconnect the old cable and unscrew the valve flange (usually 4 bolts).
- Install a new Valterra EZ Valve (part # T58B)—a direct-fit upgrade praised by RV technicians for its reliability.
- Reconnect the cable or switch to a manual twist valve for better control.
✅ Real-World Example: John M., a full-time RVer from Arizona, replaced his original valve in 2024 after 17 years of service. “It took 45 minutes and $65. No more guessing if the tank was open!”
🔧 Fix #3: Repairing Cracked or Collapsed Drain Pipes
ABS pipes under the chassis can sag or crack due to vibration and poor support.
Solution:
- Cut out damaged section with a PVC pipe cutter.
- Use 3-inch ABS couplings and primer/cement to install a new segment.
- Add pipe hangers every 18 inches to prevent future sagging (per RVIA standards).
📏 Note: The standard grey drain pipe diameter in 2007 Tiffins is 1.5 inches for sinks and 2 inches for showers.
Maintenance Tips to Prevent Future Issues
| Task | Frequency | Why It Matters |
|---|---|---|
| Flush tank with enzyme cleaner | Every 3 months | Breaks down grease & soap scum |
| Inspect gate valve operation | Before each trip | Catches cable wear early |
| Check roof vent cap | Annually | Prevents vacuum lock during draining |
| Pour 1 gallon hot water down drain weekly | Weekly | Keeps P-trap filled & lines clear |
Enzyme treatments like Green Gobbler RV Drain Cleaner are safe for plastic tanks and far more effective than bleach or lye-based products.
When to Call a Professional
While many fixes are DIY-friendly, seek expert help if:
- You suspect a tank crack (look for persistent dampness near seams)
- The floor above the tank feels soft (sign of long-term leak damage)
- You lack tools or confidence working under the chassis
Certified RV technicians follow RV Industry Association (RVIA) standards, ensuring repairs meet safety codes. Find one via the RV Safety & Education Foundation.
FAQ Section
Q1: Can I use a plunger on my RV grey tank sink?
A: Yes—but only if the tank valve is closed. Plunging with the valve open won’t create pressure. Use gentle strokes to avoid damaging seals.
Q2: Why does my grey tank smell even when empty?
A: The odor likely comes from a dry P-trap. Pour 2 cups of water down each drain monthly to maintain the water seal that blocks sewer gases.
Q3: Is it safe to dump grey water on the ground?
A: No. Even though it’s “grey,” it contains contaminants. Always dump at approved stations. Illegal dumping can result in fines—up to $5,000 in some national forests.
Q4: How long do grey tank valves last?
A: Typically 10–15 years. The 2007 Tiffin is well past that window. Proactive replacement prevents roadside emergencies.
Q5: Can I add a second vent to improve drainage?
A: Yes! Many owners install an Air Admittance Valve (AAV) under the sink. It equalizes pressure without roof modifications—just ensure it’s rated for RV use.
Q6: Where is the grey tank located in a 2007 Tiffin Allegro?
A: Usually under the bathroom or rear bedroom, centered along the chassis. Consult your owner’s manual or look for the dump valve handle on the driver’s side exterior panel.
Conclusion
Knowing how to fix the plumbing on 2007 Tiffin Grey Tank empowers you to keep your motorhome running smoothly—saving hundreds in repair bills and avoiding stressful breakdowns. From unclogging drains to replacing aging valves, these proven steps work for both weekend warriors and full-time travelers.
Your 2007 Tiffin still has years of adventure left. With proper care, its plumbing system can keep up!
👉 Found this guide helpful? Share it with fellow RVers on Facebook or Pinterest! A quick share could save someone a soggy mess on the road. Safe travels! 🚐💨
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