How To Blow Water Out Of RV Lines: The Professional Guide To Compressed Air Winterization

Blowing out RV water lines requires an oil-free air compressor regulated to a maximum of 40 PSI to purge moisture from PEX tubing and plumbing fixtures. This pneumatic method ensures that residual water does not freeze and expand, preventing catastrophic pipe bursts and valve failures during sub-zero temperatures. Success depends on the systematic isolation of the water heater and the sequential opening of every faucet, toilet, and low-point drain until only dry air is expelled.

Essential Gear and Plumbing Infrastructure Assessment

Before initiating the blowout process, you must verify the integrity of your RV’s plumbing system and gather the specific pneumatic tools required for a contaminant-free purge. Using the wrong equipment—specifically high-pressure industrial compressors without regulators or oil-lubricated units—can lead to ruptured fittings or the introduction of toxic hydrocarbons into your potable water system.

Preparation involves understanding your rig's specific layout, including the location of the water heater bypass valves, the low-point drains, and any secondary appliances like outdoor showers, ice makers, or washing machines. The goal is to create a closed loop that can be pressurized and then strategically vented to evacuate all liquid.

Required Equipment and Standards Checklist:

• Oil-Free Air Compressor: Must be an oil-less model to prevent aerosolized lubricants from entering the fresh water lines.
• Pressure Regulator: A dedicated inline regulator is mandatory to ensure the pressure never exceeds 40-50 PSI.
• Blowout Plug/Adapter: A brass or plastic fitting with a male city water connection on one end and either a Schrader valve (tire stem) or a quick-connect pneumatic fitting on the other.
• Adjustable Wrench or Socket Set: Specifically for removing the water heater drain plug (typically 1-1/16 inch for Suburban or a 1/2-inch NPT for Atwood/Dometic).
• Propylene Glycol (RV Antifreeze): Though this is a blowout guide, a small amount is required for P-traps and waste tanks.
• Estimated Duration: 45 to 90 minutes depending on the complexity of the RV’s plumbing.
• Budget Benchmark: $50–$150 if purchasing a portable compressor; $15–$25 for the adapter and antifreeze alone.

Systematic Execution of the RV Blowout Procedure

The efficacy of blowing out water lines is dictated by the sequence of operations. Skipping the water heater bypass or failing to clear the toilet valve are the two most common reasons for winterization failure. Follow these steps meticulously to ensure a dry, safe plumbing network.

Step 1: Tank Evacuation and System De-pressurization

Begin by emptying the fresh water holding tank, the grey water tank, and the black water tank at an approved dump station. Once the tanks are empty, turn off the 12V water pump and disconnect any external city water hoses. Open all interior faucets briefly to relieve the remaining pressure in the lines. If your RV is equipped with an internal water filter, remove the canister and the filter element. Replace the empty canister to maintain the continuity of the plumbing line, as the filter element will obstruct air passage and retain water.

Step 2: Draining the Water Heater and Activating the Bypass

Warning: Never attempt to drain the water heater while it is hot or under pressure. Ensure the electric heating element is switched off and the propane burner has been inactive for at least two hours to prevent scalding.

Locate the exterior water heater access panel. Open the Pressure Relief Valve (T&P valve) at the top of the tank to allow air in, then remove the drain plug at the bottom. Once the tank is empty, locate the bypass valves behind the water heater unit inside the RV. In a three-valve system, close the cold inlet and hot outlet valves and open the bypass bridge valve. In a single-valve system, turn the handle to the "Bypass" position. This step is critical; blowing air directly into a full or empty water heater tank is inefficient and can damage the tank’s internal lining.

Step 3: Connecting the Pneumatic Adapter

Attach your blowout plug to the City Water Inlet. If you are using a compressor with a tank, pre-set the regulator to 35 PSI before connecting the hose. If using a small portable 12V compressor, connect the chuck to the Schrader valve on the blowout plug.

Pro-Tip: Do not use high-pressure settings. Most RV plumbing is rated for 60-100 PSI, but the plastic fittings and gaskets at the faucets are far more vulnerable. A steady 30-40 PSI is sufficient to move water without stressing the PEX crimps.

Step 4: Sequential Line Purging

With the air compressor running and the system pressurized, go to the faucet furthest from the city water inlet (usually the rear bathroom or kitchen). Open the "Cold" side of the faucet and wait for the sputtering to stop and for a steady stream of air to emerge. Close the "Cold" side and repeat with the "Hot" side. Move through the RV, repeating this process for every fixture:

1. Kitchen Sink (Hot and Cold)
2. Bathroom Sink (Hot and Cold)
3. Shower Head (Lower the shower head to the floor to ensure no water remains in the hose)
4. Toilet (Hold the flush pedal/lever until only air is heard)
5. Outdoor Shower or Kitchen
6. Low-Point Drains (Open these last to catch any remaining pooling water)

Step 5: Appliance-Specific Clearing

Standard faucets are simple, but appliances require extra attention. If you have an ice maker, you must cycle the solenoid valve while the lines are pressurized to clear the small-diameter tubing. For washing machines, run a "Warm" fill cycle for 30 seconds to clear both the hot and cold inlet valves, then initiate a "Spin/Drain" cycle to evacuate the pump.

Step 6: Final Moisture Extraction and Trap Protection

Turn off the compressor and disconnect the blowout plug. Pour approximately 2 to 3 cups of RV-approved non-toxic antifreeze down every drain (kitchen, bathroom, shower) to fill the P-traps. This prevents sewer gases from entering the RV and protects the traps from freezing. Pour any remaining antifreeze into the toilet bowl to keep the rubber seal lubricated and prevent it from drying out or freezing to the blade.

Pressure Thresholds and Technical Hardware Specifications

Using the correct pressure and hardware is the difference between a successful winterization and an expensive repair bill in the spring. The following table outlines the technical parameters for common RV plumbing components during the blowout process.

Resolving System Obstructions and Pressure Losses

Even with a systematic approach, technical issues can arise during the blowout procedure. Understanding the root cause of these malfunctions allows for immediate field correction.

• Symptom: Air compressor runs continuously but no pressure builds in the lines.

  
  
  
  • Root Cause: The water heater bypass is incorrectly set, allowing air to fill the 6-10 gallon water heater tank, or a low-point drain remains open.
  • Actionable Fix: Re-verify the bypass valve orientation. If the valves are correct, check the exterior shower and city water connection for leaks or open valves.

• Symptom: Mist or water droplets continue to spray from faucets after extended blowing.

  
  
  
  • Root Cause: Water is trapped in the belly of the PEX lines (low spots) or the water heater was not fully bypassed, allowing moisture to bleed back into the system.
  • Actionable Fix: Close all faucets and allow the compressor to reach its maximum set pressure (40 PSI). Open one faucet at a time in a "burst" fashion to use high-velocity air to push pooled water over the internal rises in the plumbing.

• Symptom: The air coming from the faucets smells of oil or chemicals.

  
  
  
  • Root Cause: Use of a lubricated (oil-bath) compressor or a contaminated air hose.
  • Actionable Fix: Immediately cease the operation. Flush the lines with a mixture of water and baking soda or a dedicated RV system cleaner. Switch to an oil-free compressor.

• Symptom: Toilet valve continues to leak water after the blowout.

  
  
  
  • Root Cause: The internal spring-loaded valve retains a small amount of water that wasn't purged because the pedal wasn't held long enough.
  • Actionable Fix: Re-pressurize the system and actuate the toilet flush mechanism repeatedly for 15-20 seconds to ensure the valve body is completely dry.

Frequently Asked Questions

Can I use a gas-powered industrial compressor to blow out my lines?

While possible, it is highly discouraged unless you have a high-quality commercial-grade moisture and oil separator and a precision regulator. Industrial compressors often introduce oil vapor and high volumes of heat which can weaken plastic PEX fittings and contaminate your drinking water.

Is blowing out the lines enough, or do I still need RV antifreeze?

In most climates, a thorough blowout is sufficient for the pipes themselves. However, you must still use RV antifreeze in the P-traps, the toilet bowl, and any waste tanks, as these areas cannot be effectively cleared with air and are susceptible to cracking.

What happens if I forget to bypass the water heater?

If you fail to bypass the water heater, you will spend a significant amount of time trying to pressurize the large tank with air. Furthermore, the air will stir up mineral deposits and "anode rod" sediment at the bottom of the tank, pushing that grit into your faucets and clogging your aerators.

Should I leave the faucets open or closed after the blowout?

After the process is complete, it is best practice to leave all faucets slightly open. This allows for any remaining microscopic amounts of moisture to expand if they freeze without exerting pressure on the valve seats or gaskets.

How do I clear the water pump using the blowout method?

The blowout method via the city water inlet does not clear the short section of line between the fresh water tank and the water pump. To clear this, you should briefly run the water pump "dry" for about 10-15 seconds after the fresh tank is empty to kick any remaining water out of the pump head and into the main lines.

Maintain Your RV's Plumbing Integrity

Properly winterizing your plumbing ensures that your first trip in the spring isn't ruined by hidden leaks or flooded cabinets. Follow these technical protocols every season to safeguard your investment and maintain the longevity of your RV's freshwater system.