How To Blow Out Swimming Pool Lines: The Definitive Technical Guide

To blow out swimming pool lines, connect a high-volume, low-pressure air source (ideally a 3 HP pool blower or a regulated air compressor set to 5–10 PSI) to the equipment pad plumbing, then systemically force air through the suction and return lines to evacuate all water. Once the lines are clear of water, seal them with rubber expansion plugs or threaded winter plugs, and create a hydrostatic air lock in the deep-end main drain. This process prevents water from freezing and expanding inside the PVC pipes, protecting your underground plumbing from catastrophic structural ruptures during winter.

Essential Equipment and Pre-Winterization Setup

When water freezes, it expands by approximately nine percent in volume, exerting up to one hundred and fifty thousand pounds per square inch of pressure. This force easily shatters Schedule forty PVC piping, which is the standard material used in modern swimming pool construction. Properly blowing out your pool lines mitigates this risk by replacing the water column inside your plumbing with pressurized air.

Before beginning the blowout procedure, you must gather specialized tools and prepare the pool's primary filtration system. Using the wrong equipment—such as an unregulated high-pressure air compressor—can damage your pool's valves, filter tanks, and underground plumbing joints.

Required Tools, Materials, and Benchmarks

• Primary Air Source: A dedicated three-horsepower pool line blower (such as a Cyclone blower) or a commercial air compressor equipped with a highly accurate pressure regulator.
• Expansion Plugs: Heavy-duty rubber winter expansion plugs (ranging from size number six to number eleven, depending on your pipe diameter, which is typically one and a half or two inches).
• Threaded Winter Plugs: Male-threaded nylon plugs with integrated rubber O-rings, or Teflon tape for sealing threaded return jet fittings.
• Skimmer Protection Devices: Threaded, hollow expansion bottles (commonly known as Gizzmos) to seal the skimmer throat while absorbing any ice expansion in the skimmer well.
• Blowout Hose Adaptor: A standard one-and-a-half-inch male National Pipe Thread (NPT) compressor adapter or a quick-disconnect pool blower hose fitting.
• Chemical Additives: Non-toxic, propylene-glycol-based pool antifreeze. Do not use automotive ethylene-glycol antifreeze, which is highly toxic to humans and pets.
• Estimated Budget: One hundred to three hundred dollars for DIY equipment purchases; seven hundred to fifteen hundred dollars in potential repair savings.
• Estimated Duration: Two to three hours of focused labor, depending on the complexity of your pool's plumbing manifold.

Step-by-Step Plumbing Evacuation and Air Lock Execution

Blowing out pool lines requires a systematic approach to isolate and clear each plumbing line individually. Attempting to blow out all lines simultaneously will dilute the air pressure, leaving pockets of water in low-lying pipe elbows where freeze damage is most likely to occur.

Step 1: Lower the Pool Water Level

Before connecting your air source, you must lower the pool's water level. If you are using a standard winter mesh cover, lower the water level to roughly six inches below the bottom of the skimmer mouth. If you are using a solid, impermeable safety cover, you can keep the water level higher, roughly three inches below the skimmer, provided you use heavy-duty winter plugs and a Gizzmo in the skimmer well. Lowering the water reduces the hydrostatic head pressure your blower must overcome to clear the lines.

Step 2: Power Down and Drain the Pad Equipment

Turn off all power to the filtration pump, pool heater, salt chlorine generator, and automated chemical feeders at the main subpanel. Trip the circuit breakers to prevent accidental remote startup. Remove the drain plugs from your pump hair-and-lint strainer basket, the bottom of the filter tank, the pool heater header, and any auxiliary chlorinators. Allow all standing water to drain completely from these components.

Warning: Failure to cut power to the pool pump can result in the pump dry-running during the blowout, which will deform the internal diffuser, melt the impeller shaft seal, and cause permanent motor damage.

Step 3: Set the Multiport Valve and Hook Up the Blower

If your filtration system utilizes a multi-port valve, turn the handle to the "Recirculate" position. This setting bypasses the sand or diatomaceous earth (DE) filter media, allowing air to flow directly from the pump basket to the plumbing lines without blowing sand or DE powder all over your pool or clogging the internal lateral assemblies.

Remove the clear lid from your pump basket. Thread your blowout adaptor directly into the pump's drain plug opening, or insert a specialized blowout cone attached to your blower hose into the pump suction inlet. Secure all fittings to ensure an airtight seal.

Step 4: Blow Out the Suction-Side Skimmer Lines

Isolate the suction side of the pool's plumbing manifold. If your system features multiple valves (such as Jandy three-way valves), turn them so that the return lines are closed and only the skimmer lines are open to the pump. Turn on the pool blower.

Within thirty seconds, you will hear a deep gurgling sound as water is pushed out of the skimmer wells. Once a continuous, violent geyser of air and fine mist shoots out of the bottom of a skimmer, quickly insert a threaded Gizzmo or a rubber expansion plug into the hole at the bottom of the skimmer. Wrap the threads of the Gizzmo with three wraps of Teflon tape to ensure a watertight seal. If you have multiple skimmers, blow them out one at a time by closing the valve of the cleared skimmer to direct maximum air volume to the remaining open lines.

Step 5: Clear the Pressure-Side Return Jets

Adjust your plumbing manifold valves to close the suction side and open the pressure (return) side of the system. Turn on the air blower. Air will begin moving toward the return jets in the pool walls.

Because air follows the path of least resistance, it will exit the return jet closest to the equipment pad first. Once you see a strong, steady stream of air bubbles escaping the first return jet, insert a rubber expansion plug or a threaded winter plug into the nozzle and tighten it securely. The air pressure will automatically shift to the next furthest return jet. Repeat this process until every return jet is cleared and plugged.

Pro-Tip: If your pool features a dedicated automatic cleaner line (such as a pressure-side Polaris sweep line), treat this as a return line. Blow it out thoroughly and seal it with a black rubber plug.

Step 6: Create a Hydrostatic Air Lock in the Main Drain

The main drain line sits at the deepest point of the pool, which presents a unique challenge. Because water weighs zero point four three three pounds per square inch per foot of depth, a ten-foot-deep pool requires at least four point three three PSI of pressure just to push the water column back down to the main drain grate.

With your blower running, turn the plumbing valves so that only the main drain line is open. You will eventually see a massive eruption of air bubbles rising from the main drain grate on the pool floor. Let this bubble for roughly fifteen seconds to ensure the water column is pushed down below the regional frost line.

Immediately turn the main drain valve to the fully closed position while the blower is still running. This actions traps the pressurized air in the vertical riser of the main drain pipe, creating an "air lock" that prevents water from rising back up the pipe, even though the drain remains open to the pool water at the bottom.

Step 7: Add Antifreeze to the Lines

As an added layer of security, turn off the blower and pour non-toxic propylene glycol pool antifreeze down the open skimmer lines and return pipes before inserting the final plugs. Use approximately one gallon of antifreeze for every fifteen to twenty feet of pipe length. This prevents any residual water droplets that pool in low elbows from freezing into solid plugs.

Technical Parameters for Pool Line Winterization

Selecting the correct equipment and operating under safe mechanical limits is vital for a successful blowout. The table below highlights the performance, safety, and compatibility parameters of the three most common air sources utilized for swimming pool line winterization.

Common Line Winterization Failures and Field Remedies

Plumbing system configurations vary wildly, and field technicians frequently encounter anomalies that prevent a clean blowout. Understanding how to diagnose and correct these failures in real-time prevents freeze damage.

Scenario 1: Air bubbles continue to escape from return jet plugs after tightening

• Root Cause: The rubber expansion plug has lost its elasticity, is incorrectly sized for the pipe wall schedule, or the PVC pipe wall has interior scale buildup preventing a flush seal.
• Actionable Fix: Remove the plug and inspect the rubber for dry rot or micro-cracks. If the plug is intact, coat the rubber contact ring with a thin layer of non-petroleum silicone pool gasket lubricant. Re-insert the plug and use a wrench to tighten the wing nut an additional two full rotations beyond finger-tight. If scale is present inside the pipe, sand the interior pipe lip with medium-grit emery cloth before re-plugging.

Scenario 2: The blower motor runs but fails to push air out of any pool lines

• Root Cause: Air is escaping through an open path of least resistance within the equipment pad, such as an open sand filter drain valve, a cracked pump basket lid gasket, or an unaligned multi-port valve.
• Actionable Fix: Turn off the blower immediately to prevent motor overheating. Inspect all equipment pad valves. Ensure that the multi-port valve is set strictly to "Recirculate" (not "Filter" or "Backwash") and verify that all equipment drain plugs (pump, filter, heater) are installed securely or that their paths are completely isolated by closed valves.

Scenario 3: Water rushes back into the skimmer line immediately after turning off the blower

• Root Cause: You did not establish a tight seal on the skimmer plug or Gizzmo fast enough, or the air lock was lost on the suction side before the plug could be threaded home.
• Actionable Fix: Turn the blower back on and wait for the skimmer to blow dry. Prepare your Gizzmo by pre-wrapping its threads with Teflon tape. While the air is actively blowing and pushing the water away, thread the Gizzmo into the suction port. Do not turn off the blower until the plug is completely sealed and tightened in place.

Frequently Asked Questions

Can I use a standard shop vac to blow out my pool lines?

A standard shop vacuum is generally insufficient for in-ground swimming pool lines because it provides high volume but lacks the static pressure (usually less than two PSI) required to push water down to deep main drains or through long, underground piping runs. While a shop vac may work on shallow, above-ground pool lines, in-ground systems require a dedicated pool blower or a regulated air compressor to safely and fully evacuate the water.

How much air pressure is safe for blowing out pool plumbing?

The maximum safe air pressure for blowing out Schedule forty PVC pool plumbing is ten to twelve PSI. You must never exceed fifteen PSI, as excess pressure can easily crack old PVC pipes, rupture brittle diverter valves, or blow the plastic lid off your pool pump, creating a hazardous projectile risk.

Do I need to put antifreeze in my pool lines after blowing them out?

While not strictly mandatory if a line is one hundred percent dry, adding non-toxic propylene glycol pool antifreeze provides a crucial safety margin against residual water. If a small amount of water seeps past a plug or condenses in a low-lying pipe elbow, the antifreeze prevents it from freezing into a solid, expanding block of ice that could crack your underground plumbing.

How do I create an air lock in the main drain line?

To create an air lock, run your blower until a continuous stream of air bubbles erupts from the main drain at the bottom of the pool. While the blower is still pressurized and running, quickly close the main drain valve at your equipment pad. This traps the air column inside the vertical pipe, pushing the water level down below the frost line and preventing it from returning, even though the bottom of the line remains open to the pool.

Protect Your Pool Investment This Winter

Protect your underground plumbing from devastating freeze expansion by executing your blowout with precision and care. If you are uncomfortable handling high-volume air systems or isolating complex plumbing manifolds, contact our certified pool service team today to schedule a professional winterization service.