How To Blow Out The Water Lines On An RV

Winterizing your recreational vehicle by blowing out the water lines with compressed air prevents catastrophic freezing damage to plumbing fixtures, pumps, and fittings during sub-freezing temperatures. By maintaining air pressure strictly between 30 and 40 PSI and systematically purging every hot and cold water valve, low-point drain, and appliance, you eliminate residual water that expands and cracks infrastructure.

Winterization Setup: Essential Equipment and Pre-Operation Planning

Successfully purging an RV plumbing system requires careful preparation and specific hardware to protect delicate PEX piping, brass fittings, and internal water heater tanks. Before introducing compressed air into the system, you must gather specialized adapters and isolate components that cannot withstand high pressure or trap standing water.

• Essential Gear & Tools: Portable air compressor with an adjustable regulator, brass or nylon blowout plug (Schrader valve adapter), non-toxic RV antifreeze (Propylene Glycol, minimum 2-3 gallons), water heater bypass kit, basic hand tools, and a towel or bucket for residual spills.
• Prerequisite Standards & Knowledge: Keep air compressor output strictly restricted to 30 to 40 PSI. Exceeding 40 PSI can instantly rupture internal lines, split threaded fittings, or blow apart factory crimp rings. Always disable and isolate the water heater before applying air to protect the tank liner and anode rod.
• Estimated Benchmarks: Duration ranges from 45 to 60 minutes for standard travel trailers and motorhomes. Total expenditure for adapters and antifreeze ranges from 30 to 60 dollars if you already own an air compressor.

Step-by-Step RV Water System Air Purge Protocol

Step 1: Drain and Isolate the Water Heater

Begin by ensuring the RV's 120V electrical power and propane supply to the water heater are completely turned off. Allow the water heater tank to cool down entirely to avoid severe scalding injuries from pressurized hot water. Open the exterior access panel, pull the pressure relief valve lever outward, and remove the exterior drain plug (or anode rod on municipal-style water heaters) to empty the tank completely.

Warning: Never apply compressed air to a water heater containing water, and never pressurize the tank without an active bypass valve engaged, as excessive pressure can rupture the vessel.

Step 2: Engage the Water Heater Bypass Valves

Locate the water heater backside plumbing assembly inside the RV, typically hidden behind cabinets, under a dinette seat, or near the utility bay. Turn the bypass valves from their normal operating position to the bypass configuration. This action isolates the water heater tank so that compressed air and RV antifreeze bypass the tank entirely, saving you from wasting gallons of antifreeze trying to fill a six- or ten-gallon basin.

Step 3: Open Low-Point Drains and Fixtures

Locate the low-point drain lines beneath the belly of your RV, usually hanging below the underbelly or accessible through an exterior utility compartment. Remove the caps or open the valves on both the hot and cold low-point water lines to let gravity evacuate the bulk of standing water. Next, walk through the interior of the RV and open every single faucet, shower valve, and flush the toilet to let ambient water drain out freely. Close the low-point drains once the bulk flow stops, but leave all interior faucets open in the half-open position.

Step 4: Attach the Compressor and Set Pressure Limits

Screw your brass blowout plug directly into the city water inlet connection on the exterior wall of the RV. Connect the hose from your air compressor to the blowout plug. Adjust your air compressor regulator so that the output gauge reads a safe, controlled pressure level between 30 and 40 PSI maximum. Never connect unregulated shop air directly to your RV city water port.

Step 5: Execute the Systematic Fixture Purge

With the compressed air flowing into the system at 30 to 40 PSI, begin purging each water fixture systematically, starting with the fixture located furthest from the city water inlet and working your way closer. Open the hot side of the furthest bathroom sink until only a fine mist or dry air emerges, then close it and repeat the process for the cold side. Move sequentially through the secondary bathroom, kitchen sink, interior shower, exterior wash station, and flush the toilet pedal or handle multiple times until no water sprays from the lines.

Pro-Tip: Do not neglect the residential-style refrigerator ice maker supply line, washing machine hookups, and the exterior shower, as these hidden branch lines frequently retain pockets of water that freeze and crack.

Step 6: Clear the Fresh Water Pump and Trap P-Traps

Turn off and unplug the air compressor, then disconnect the blowout plug from the city water inlet. Locate your 12-volt water pump, remove the inlet screen/filter bowl, and empty any standing water. Briefly switch the water pump on for three to five seconds with all faucets closed to force remaining water out of the internal pump diaphragm, then switch it immediately back off to prevent dry-motor damage. Pour a half-cup of RV-specific antifreeze down every drain trap (sink and shower P-traps) and into the toilet bowl to protect the gray and black tank holding valve seals from freezing.

Winterization Method Comparison: Compressed Air Versus Antifreeze

Common Site Failures and Field Fixes

• Root Cause: Water continues to pool in the low-point lines or a specific faucet despite repeated air purges.
  
  
  • Actionable Fix: The RV is likely parked on a slight slope, preventing gravity from draining low points completely. Relocate the RV to a level surface, open the low-point drains again, and re-apply compressed air pulses to force the trapped fluid upward and out of the lines.
• Root Cause: Air pressure drops rapidly during the fixture purge, failing to clear lines effectively.
  
  
  • Actionable Fix: You are opening too many valves simultaneously or your compressor tank is too small. Keep only one faucet open at a time, allow the compressor tank to recharge fully between fixtures, and check all quick-connect fittings for pneumatic air leaks.
• Root Cause: The fresh water pump fails to prime or leaks when reactivated in the spring.
  
  
  • Actionable Fix: Residual water inside the pump housing froze because the internal diaphragm was not purged or protected with antifreeze. Disassemble the pump head, inspect the rubber valves for cracks, and replace the pump assembly if structural housing splits are visible.

Frequently Asked Questions

What is the safest air pressure setting for blowing out an RV water lines?

Maintain your compressor output strictly between 30 and 40 PSI. PEX tubing can withstand higher pressures, but factory crimp rings, plastic barbed fittings, and threaded shower valve bodies can fracture under pressures exceeding 50 PSI.

Do I still need RV antifreeze if I use compressed air?

While compressed air removes the vast majority of water from the main lines, it does not guarantee complete evacuation of the freshwater pump housing, holding tank valves, and sink P-traps. Pouring a small amount of non-toxic RV antifreeze down the drains and into the pump ensures those vulnerable components remain completely protected.

Should the water heater bypass be engaged before blowing out lines?

Yes, absolutely. Engaging the bypass valves prevents water, compressed air, and antifreeze from entering the water heater tank, which protects the tank lining, saves you from wasting gallons of fluid, and prevents pressure spikes inside the vessel.

How do I clear water out of the toilet and refrigerator ice maker?

Depress the toilet flush pedal while the compressed air system is pressurized until only air sprays out. For refrigerators equipped with an ice maker, you must manually cycle the water solenoid valve open using a jumper wire or follow the manufacturer's diagnostic mode instructions to blow air through the ice maker supply line.

Protect your investment this winter by properly draining and winterizing your RV plumbing system today.