Electrical and Systems
RV Black and Gray Holding Tank Repair and Replacement
Typical range
$750 to $8,500
Shop hours
5 to 35
Labor rate
$260/hr
The short answer
Holding tank work covers cracked and leaking tanks, broken dump valves, failed flanges and seals, sensor problems, and full tank replacement. Work runs $750 to $8,500, or 5 to 35 hours at $260 per hour plus parts, including underbelly removal and reinstallation.
01
What this work actually involves
Holding tanks fail at their mounting and at their fittings far more often than they fail in the middle of a wall. A full black tank weighs several hundred pounds and it hangs from straps or a cradle under the floor, so every freeway expansion joint on the 91, the 15, and the 60 works that mounting. Straps fatigue, the tank sags, and the stress concentrates at the ABS flange where the dump line attaches. That flange is what usually cracks, and the leak runs down the inside of the underbelly where nobody sees it for months.
Dump valves are the other regular failure. The blade seal hardens and the valve either will not seal, which fills the dump line and surprises you when the cap comes off, or it will not open because the cable has corroded and seized. Coastal storage in Long Beach and Oceanside corrodes cable actuators quickly. Low desert heat in Palm Desert and Indio hardens the seals faster than the rest of the state. Both failure paths end with a valve that has to come out, and on many coaches that means dropping the underbelly to reach it.
Tank level sensors deserve a plain answer: the factory probe style sensors read wrong because waste and paper bridge the probes, and no amount of tank cleaning permanently fixes that. If accurate levels matter to you, the answer is an external sensor system that reads through the tank wall, installed while the underbelly is already open. We will tell you that up front rather than charging for repeated tank flushes that solve it for a week.
Systems and brands we work on: Thetford, Dometic, Furrion.
Location: All work is performed at our Yorba Linda facility. We do not offer mobile, roadside, or fleet route service.
02
What the job includes
- Underbelly removal, insulation handling, and correct reinstallation
- Cracked and leaking polyethylene and ABS tank repair or replacement
- Tank strap, cradle, and mounting repair and reinforcement
- Dump valve, blade seal, and cable actuator replacement
- Flange, elbow, and dump line repair at the failure point
- Toilet flange and floor seal replacement where the leak is at the top
- Vent stack clearing and roof vent repair for tank ventilation
- Probe sensor cleaning and external through-wall sensor system installation
- Tank flush system installation and repair
- Pressure and fill testing of the completed system before delivery
03
When you need this service
- Odor under or around the coach that is worse after driving
- Wet or sagging underbelly material below a tank
- Dump valve that will not open, will not close, or leaks past the blade
- Waste in the dump line before the valve is opened
- Tank level readings that never change or read full when empty
- Slow drains and gurgling at fixtures, indicating a blocked vent
- Visible cracking around the dump flange or at a strap contact point
04
How we do it, step by step
- 01
Locate the actual leak
Tanks are filled and inspected with the underbelly opened where required. Leaks travel along the underbelly, so the wet spot and the crack are frequently in different places.
- 02
Mounting and strap inspection
Straps, cradle, and support checked under load. A sagging tank puts all its stress into the dump flange, which is why the flange is usually what cracks.
- 03
Valve and line assessment
Dump valves cycled and inspected, blade seals and cable actuators checked, and the dump line and elbows examined for cracks and prior repairs.
- 04
Repair versus replace pricing
We price a welded tank repair against a replacement tank honestly. A crack at a strap contact point on an old tank usually means the next crack is already forming nearby.
- 05
Repair and reinforcement
Tank repaired or replaced, straps and cradle rebuilt or reinforced, and the flange supported so the mounting rather than the fitting carries the load.
- 06
Test and close up
Tanks filled and held to check for leaks, valves cycled, vent path verified, and the underbelly reinstalled properly with insulation restored.
05
Pricing and posted rates
| Item | Rate or range | Notes |
|---|---|---|
| Typical job range | $750 to $8,500 | Varies with extent of damage and parts availability |
| Shop hours | 5 to 35 | Quoted after teardown, not before |
| Mechanical and electrical labor | $260 per hour | 2026 posted rate |
| Parts | 100% markup under $100, 35% over | Special order parts require a non refundable deposit at order |
| Deposit | 50% at authorization over $2,000 | Additional 25% when parts arrive on jobs over $10,000 |
| Sales tax | 7.75% on parts and materials | Labor is not taxed |
Insurance billed jobs may be billed at carrier negotiated labor rates that differ from the posted retail rates above. See all posted rates.
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Vehicles we do this work on
Vehicle
Class A Gas Motorhomes
A Class A gas motorhome is a flat-front coach built on a Ford F53 or Workhorse front-engine chassis, typically 28 to 38 feet. Rear
Vehicle
Class C Motorhomes
A Class C is a coach body built onto a cutaway van chassis with a sleeping or storage cabover extending above the factory cab. Tha
Vehicle
Standard Fifth Wheels
A fifth wheel couples to a hitch in the truck bed through a kingpin and pin box, with a raised forward bedroom over the truck. The
Vehicle
Travel Trailers
A travel trailer tows from a ball hitch behind the tow vehicle rear axle on an A-frame tongue, which makes it the most sway-prone
Vehicle
Toy Hauler Fifth Wheels
A toy hauler fifth wheel carries a cargo garage behind the axles with a full-height rear ramp door. Load behind the axle centerlin
Vehicle
Truck Campers, Slide-In
A slide-in truck camper sits in a pickup bed and is clamped down at four points, so it absorbs the truck frame twist directly. Jac
Vehicle
Park Model RVs
A park model is a towable unit up to roughly 400 square feet built with residential windows, roofing, and finishes, designed to si
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Questions about black and gray tank repair and replacement
Frequently asked questions
How much does RV holding tank replacement cost?
Work runs $750 to $8,500, or 5 to 35 hours at $260 per hour plus parts. A dump valve and seal replacement with easy access is at the low end. A full black tank replacement requiring underbelly removal, strap fabrication, new flange and dump line, and reinstallation of insulation and coroplast is at the high end.
Why do my tank level sensors always read wrong?
Because the factory probe sensors read continuity through the tank wall contacts, and waste and paper bridge across them permanently. Tank cleaning fixes it temporarily at best. The real solution is an external sensor system that reads through the tank wall from outside, which we install while the underbelly is already open for other work.
My black tank smells but I cannot find a leak. What now?
Check the vent before the tank. A blocked roof vent stack forces tank gas to find another way out, usually up through a dry toilet seal or a shower trap. Wasps and debris block vent stacks routinely on stored coaches. The other common source is a failed toilet flange seal at the floor, which smells without ever dripping.
Can a cracked tank be repaired or does it need replacing?
Polyethylene tanks can be plastic welded, and where the crack is isolated and the tank is otherwise sound that is a reasonable repair. Where the crack is at a strap contact point on an aged tank, replacement is the better value, because the same fatigue is already working on the adjacent area. We price both and explain which applies.
Why does my dump valve leak into the line?
The blade seal has hardened and no longer seals against the blade. Low desert heat accelerates that considerably. It is a straightforward part but on many coaches the valve is behind the underbelly, so the access is what drives the labor. While we are in there we check the second valve and the flange rather than going back twice.
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Ready to move on black and gray tank repair and replacement? Bring it to Yorba Linda.