RV Plumbing, Tank, and Pump Repair

Supply plumbing and the fittings that betray it

Modern coaches plumb in PEX, which is durable, tolerant of a hard freeze, and easy to repair correctly. The weak point is never the tubing. It is the connection. Crimp rings need a full circumference compression checked with a go-no-go gauge, cinch rings need the right jaw, and push-to-connect fittings depend on a clean square cut and an insert that seats fully. A joint that was slightly out of round when it was made will hold pressure for a year and then start weeping under road vibration.

Older units, particularly from the 1980s and 1990s, may still carry gray polybutylene with acetal fittings. That combination becomes brittle with age and chlorine exposure, and it cracks at the fitting shoulder with essentially no warning. If we find it during any other job, we say so, because piecemeal repair of polybutylene tends to be a series of visits. Replacing the runs with PEX during work that already has the walls or floor open is dramatically cheaper than doing it as its own project.

City water pressure is the load that finds every weak joint. Campground pressure varies enormously and can spike well above what an RV system is designed for, and a regulator at the inlet is the cheapest insurance in the hobby. Many owners use an adjustable regulator and set it too high. We set it at the inlet, verify actual delivered pressure with a gauge at a fixture, and check the backflow preventer at the city water connection while we are there, since a failed check valve pushes city pressure into the tank and overflows it.

Water pumps, accumulators, and pulsation

Diaphragm pumps from Shurflo, Aquatek, and Remco are positive displacement units that build pressure until an internal switch opens. When that switch contact pits or the diaphragm develops a pinhole, the pump short cycles: a rapid tick-tick-tick with no water drawn. Owners often diagnose that as a leak in the system, and sometimes it is, but an internal check valve that no longer seats produces the same symptom without a drop leaving the coach. Isolating the pump from the system tells you which in about a minute.

Pulsation is the other complaint. A bare pump cycles on and off many times a minute against a small draw, which is noisy and hard on the switch. An accumulator tank, essentially a small pressurized bladder, absorbs the pressure swing and lets the pump run in longer, quieter cycles. Precharging that bladder to just under the pump cutoff pressure is what makes it work, and a great many installed accumulators have lost their charge entirely and are doing nothing at all.

Priming failures are usually on the suction side rather than in the pump. A cracked fresh tank pickup fitting, a collapsed suction hose, a clogged strainer, or a tank vent that has been blocked by a nest will all leave a healthy pump unable to draw. We check suction before condemning a pump, because the pump is the expensive part and the strainer is a two dollar screen. Dry running for any length of time does damage the diaphragm, so a pump that has been left switched on with an empty tank frequently needs both repairs.

Holding tanks, valves, and the sensor problem

Holding tanks are usually rotationally molded polyethylene or fabricated ABS, hung in straps or cradled on a frame. They fail at the mounting points and at the fittings rather than in the middle of a wall. A tank that has been run heavy and unsupported will sag, stress the flange where the dump pipe joins, and crack there. Repair on polyethylene is genuinely difficult because most adhesives will not bond to it, so plastic welding or replacement are the real options, and we say which one applies after seeing it.

Dump valves are simple and they are neglected. A Valterra style blade valve seals against two rubber gaskets, and grit riding on the blade cuts those gaskets over time. The result is a valve that seems closed but slowly fills the sewer hose, which people discover when they pull the cap. Replacing seals is inexpensive when the flange bolts come apart cleanly, and a nightmare when they have corroded solid, which is why we quote it after inspection rather than from a phone description.

Level sensors deserve their reputation. Traditional probe sensors read continuity through the waste, so a film of tissue and residue bridging a probe reports full forever. No amount of rinsing from the toilet fixes this reliably. The genuine fixes are a thorough tank cleaning with a rotating wand through the toilet flange, or a conversion to an external sensor that reads through the tank wall and never touches the contents. We do both and recommend the second on any tank that has already been chronically wrong.

Macerator systems such as the Sani-Con add a grinder pump so waste can be pushed uphill through a small hose. They are convenient and they are intolerant of anything that is not waste and paper. Wipes, feminine products, and hard debris jam the impeller and burn the motor. Most units have a manual release for a jam, and knowing where it is saves a service call. When the motor has already burned, replacement is straightforward and we install a cleanout in the discharge line so the next jam is a five minute job.

Drains, vents, and where odors really come from

A persistent sewer odor inside the cabin almost never means the tank needs more chemicals. It means a trap has lost its water seal or the vent stack is not doing its job. Every drain has a P-trap holding a plug of water that blocks gas, and traps evaporate dry during storage or siphon empty when a large flow pulls past them. Pouring a cup of water into each drain rules that out in five minutes and is the first thing worth trying.

The roof vent stack lets air into the system so drains do not pull their own traps empty. A stack that has been crushed, capped by a repair, blocked by a nest, or terminated too close to a window creates both slow drains and odor that comes back down into the living space. On some floorplans the toilet vent runs through a wall cavity where a previous repair pinched it, and finding that is a matter of tracing rather than guessing.

The toilet flange seal is the other frequent source, and it is the one that also causes structural damage. The closet flange sits on the floor and the toilet compresses a seal against it. When the seal hardens or the flange bolts loosen, waste water wicks into the plywood underneath the toilet base, where nobody sees it until the floor is soft. Any odor complaint that centers on the bathroom gets a floor probe as part of the diagnosis, because the plumbing repair is cheap and the subfloor repair is not.

What is included

Pressure test of the supply system

System brought up and held so slow weeps behind panels show themselves before we open anything.

Fitting and connection rework

Crimp rings gauged, push-to-connect joints reseated, and aged polybutylene runs identified and quoted.

Pump, switch, and accumulator service

Diaphragm and check valve condition, switch behavior, and accumulator precharge set to match cutoff.

Tank repair or replacement

Plastic welding where the material allows it, new tank and straps where a cracked flange has compromised the mount.

Dump valve and seal replacement

Blade valve seals, flange gaskets, and cable actuators renewed, with seized hardware handled as its own line.

Sensor cleaning or external conversion

Wand cleaning through the flange, or a sensor set that reads through the tank wall and cannot foul.

Signs you need this work

• The water pump ticks on and off every few seconds with no tap open
• A tank that reads full immediately after a complete dump
• The sewer hose fills up before the valve is pulled
• A soft or spongy spot in the floor near the toilet base
• Sewer odor inside the cabin that gets worse after the unit has been stored
• Water pressure that drops to a trickle when two fixtures run together