Winterizing an RV without wrecking the plumbing

What freeze damage actually does

Water expands as it freezes, and in a closed pipe that expansion has nowhere to go. The result is split PEX, cracked fittings, a fractured water pump head, or a split water heater tank. None of it is visible in winter. You discover it in spring when you pressurize the system and water appears inside a wall.

The repair cost is not really about the plumbing parts, which are cheap. It is about the access, because RV plumbing runs behind cabinetry, under floors and inside walls that were assembled before the interior went in.

Before you start

Gather what you need first, because the process goes badly if you stop halfway through. You want RV-specific non-toxic antifreeze, which is propylene glycol based and safe for potable systems. Do not use automotive antifreeze under any circumstances: ethylene glycol is toxic.

Decide on your method. Blowing the lines out with compressed air is faster and uses no antifreeze, but it is harder to be certain you got everything, particularly traps and the toilet valve. Pumping antifreeze through the system is more thorough and is the safer default for anyone doing it for the first time. Many owners do both.

The sequence

Order matters here. Draining before bypassing, or adding antifreeze before draining, wastes product and leaves water behind.

1. Drain and flush the black and gray tanks completely, then close the valves.
2. Turn off the water heater and let it cool fully. Never drain a hot pressurized tank.
3. Drain the fresh water tank and open all low-point drains, both hot and cold.
4. Relieve water heater pressure, then remove the drain plug or anode rod and let the tank empty. Flush it with a wand while it is open.
5. Set the water heater bypass valves to bypass, so antifreeze does not fill the six gallon tank needlessly.
6. Close the low-point drains and refit the water heater plug or anode rod.
7. Connect the pump to the antifreeze supply, either through the built-in winterizing inlet or by dropping the intake hose into a jug.
8. Run the pump and open each fixture one at a time, hot then cold, until antifreeze runs steadily. Work from nearest the pump to farthest.
9. Do not forget the toilet, the outside shower, the icemaker line and the washing machine connections if fitted.
10. Pour a cup of antifreeze down every drain to fill the P-traps, and a cup into the toilet bowl.
11. Bypass or drain any inline water filter, and remove the filter cartridge.

The mistakes that cause the damage

Almost every winterizing failure traces back to one of a small number of specific omissions, and they repeat year after year across owners.

• Leaving the water heater unbypassed, which fills the tank with antifreeze and wastes several gallons, or worse, leaving it undrained so it freezes and splits
• Missing the P-traps, which hold water even when the lines are empty
• Forgetting the outside shower, which is out of sight and holds water in a long run of hose
• Leaving an inline filter cartridge in place, which cracks when the water inside it freezes
• Failing to drain the fresh water tank itself, on the assumption that the lines are what matters
• Storing with the low-point drains closed and no antifreeze, leaving residual water trapped at the low points

De-winterizing without breaking anything

Spring is where the second set of expensive mistakes happens. Reverse the process carefully.

Set the bypass valves back to normal operation. If you skip this, you will have no hot water no matter what else you do, and it is the single most common spring service complaint.

Fill the fresh tank and flush the system until the antifreeze is gone and the water runs clear and odorless. Then sanitize the fresh water system with a diluted bleach solution or a proprietary sanitizer, let it dwell, and flush thoroughly.

Fill the water heater and confirm water flows steadily from a hot tap before you switch on the electric element. An element energized in an empty tank burns out within seconds, and it is entirely avoidable.