How To Blow Out Your Pool Lines: Step-by-Step Winterization Manual

Evacuating water from your swimming pool's plumbing infrastructure using high-volume air injection is the single most critical step in preventing catastrophic freeze-expansion ruptures in underground Schedule 40 PVC pipes. This process requires forcing continuous low-pressure air (typically 3 to 4 PSI from a dedicated pool blower or a regulated 10 to 15 PSI from an air compressor) through suction and return loops until all moisture is displaced, followed immediately by installing airtight expansion plugs and creating an air lock on main drains.

Essential Equipment, Safety Tolerances, and Pre-Winterization Setup

Blowing out pool lines requires specific high-volume air delivery tools rather than raw high pressure. Standard home shop compressors yield high pounds per square inch (PSI) but low cubic feet per minute (CFM), which can lead to pipe over-pressurization without moving enough volume to push water up and out of deep lines. A dedicated 3-horsepower pool line blower delivering 100 to 140 CFM at low pressure is the industry standard for complete moisture displacement.

Before starting the purging process, verify that your pool water chemistry is balanced (pH 7.2–7.6, Total Alkalinity 80–120 ppm, and Chlorine 1–3 ppm) and that shock treatment has fully circulated to prevent algal blooming under winter covers.

Essential Gear & Hardware

• Air Delivery Source: Commercial pool blower (e.g., 3-HP Cyclone) or a regulated air compressor with a quick-connect blow-thru adapter.
• Expansion Plugs: Heavy-duty straight and tapered rubber expansion plugs (NPT Sizes #7 through #11) with stainless steel wing nuts.
• Freeze Protection Accessories: Standard 16-inch or long-stem Gizzmos (threaded skimmer freeze compensators) with intact Teflon tape on threads.
• Chemical Additives: 1 to 3 gallons of non-toxic, virgin propylene glycol pool/RV antifreeze (never use toxic ethylene glycol automotive antifreeze).
• Hand Tools: Filter drain plug wrench, channel-lock pliers, strap wrench, and thread sealant tape (PTFE).

Pre-Procedure Benchmarks

• Estimated Duration: 1.5 to 3.0 hours depending on pool volume, line complexity, and attached features (spas, deck jets, waterfalls).
• Pressure Thresholds: Maximum 15 PSI when using an air compressor; continuous 3 to 5 PSI when using a high-CFM centrifugal blower.
• Budget Range: $50 to $250 for DIY equipment adapter kits and chemical antifreeze, compared to $300 to $600 for professional service calls.

Step-by-Step Pool Line Clearing and Deep Freeze Protection Workflow

Step 1: Lower Pool Water and Isolate Equipment Pad

1. Submersible pump or backwash the pool water level to 4 to 6 inches below the bottom of the tile line or below the lowest skimmer mouth. If using an Aquador skimmer cover plate, water can remain at normal operating levels, though dropping water below the skimmers remains the safest method.
2. Shut off main power to the pool pump, heater, salt chlorinator, and automated control boards at the primary circuit breaker.
3. Remove all drain plugs from the pump strainer housing, filter tank, heater header, booster pump, and inline chlorinator. Store these plugs inside the pump strainer basket for winter safety.
4. Set the filter multiport valve (MPV) to the Recirculate position to bypass the filter media, or set it to Closed if blowing directly into dedicated plumbing ports.

Warning: Never attempt to blow out pool lines through a DE or sand filter tank while the multiport valve is set to "Filter." High volume air can burst the filter tank, crack grid manifolds, or ruin internal lateral assemblies under pressure.

Step 2: Connect the Air Delivery System

1. Thread a 1.5-inch or 2-inch blow-thru plug adapter directly into the pump's front intake housing, the pump drain plug port, or the discharge side of the pump depending on your plumbing manifold design.
2. If using a compressor, set the regulator output knob to maximum 15 PSI before connecting the hose quick-disconnect fitting to the adapter.
3. Connect your pool blower hose securely to the blow-thru fitting, ensuring an airtight seal with thread tape if necessary.

[ Air Blower / Compressor ] │ ▼ [ Blow-Thru Threaded Adapter ] │ ▼ ┌─────────────────> [ Pump Strainer Housing ] <─────────────────┐ │ │ ▼ ▼ [ Suction Lines ] [ Discharge Lines ] ├── Skimmer Line 1 (Plug/Gizzmo) ├── Return Line 1 (Plugged) ├── Skimmer Line 2 (Plug/Gizzmo) ├── Return Line 2 (Plugged) └── Main Drain (Air-Locked Valve) └── Water Features (Plugged)

Step 3: Evacuate the Suction Lines (Skimmers and Main Drain)

1. Turn all suction valves on your intake manifold to the open position except one skimmer line. Close the main drain valve completely to direct full air volume to the open skimmer.
2. Power on the air blower. Air will force water through the pipe out into the skimmer well inside the pool.
3. Allow air to blast out of the skimmer for 30 to 60 seconds until only a fine mist/vapor escapes, indicating the pipe is empty.
4. Pour 1/2 gallon of non-toxic propylene glycol pool antifreeze directly down the clear skimmer pipe, then thread a Teflon-taped Gizzmo tightly into the bottom inlet port of the skimmer.
5. If operating a dual-skimmer system, turn the intake valve to isolate the cleared skimmer and open the second skimmer line. Repeat the blowing and sealing process.
6. Open the main drain valve on the manifold while closing all skimmer valves. Watch the deep end of the pool for heavy bubbling over the main drain grate.
7. Once strong, violent bubbling occurs at the bottom of the pool (confirming air has pushed water all the way down the pipe), quickly slam the main drain diverter valve to the Off position while the blower is actively running.

Pro-Tip: Closing the main drain valve while air is actively purging creates a permanent "air lock." Because air is lighter than water, the trapped air pocket holds the water column down inside the vertical pipe far below the frost line, eliminating the need to plug the main drain at the pool floor.

Step 4: Clear Return Lines, Water Features, and Auxiliary Equipment

1. Move the air source to the discharge side of the pump or shift your 3-way distribution valves to route air toward the pool returns.
2. Open the valve for the primary pool return line loop while keeping auxiliary feature valves (waterfalls, deck jets, sheer descents) closed.
3. Air will purge water out through all wall return fittings simultaneously. Because air follows the path of least resistance, the return closest to the equipment pad will purge first.
4. As air blasts dryly out of the closest return fitting, tightly insert a rubber expansion plug (#8, #9, or #10 depending on pipe size) into the wall fitting and tighten the wingnut clockwise until secure.
5. Watch as the air redirects down the line to purge the next closest return fitting. Repeat this process, plugging each fitting sequentially from closest to furthest from the pad.
6. For the final return fitting, turn off the air blower, pour 1/4 gallon of propylene glycol antifreeze into the wall eyeball fitting using a flexible funnel, then install the final rubber expansion plug firmly.
7. Open auxiliary feature valves (laminars, waterfalls, spa jets) one at a time and run the blower until each feature spits pure air. Plug each line or turn off its specific diverter valve to lock the air in place.

Warning: High-end water features like sheer descents and laminars contain delicate internal baffles that can warp or rupture if subjected to pressures over 5 PSI. Always use high-volume blowers rather than air compressors when clearing these components.

Step 5: Protect Pad Equipment and Lock Out Mechanicals

1. Disconnect the air blower setup from the plumbing manifold.
2. Pour 1/2 gallon of pool antifreeze directly into the top of the pump housing to protect any residual water trapped inside lower chamber pockets.
3. Turn the filter multiport valve handle so it sits midway between two designated notches (e.g., between "Winter" and "Closed", or resting on top of a setting divider). This lifts the internal spider gasket off its seating face, preventing freeze-adhesion and flat-spotting over winter.
4. Leave all lower equipment drain plugs removed. Store them safely inside the pump basket, and put the pump lid loosely back on to keep debris out while allowing air circulation.

Technical Air Delivery Parameters and Equipment Compatibility Matrix

Choosing between an air compressor and a high-volume pool blower impacts purging efficiency and system structural safety. Use the metrics below to align equipment capabilities with your pool’s specific plumbing design.

Field Failures, Underground Leak Diagnostics, and Immediate Remedies

Scenario 1: Persistent Water Bubbling in Skimmer After Installing Plugs

• Root Cause: The expansion plug rubber has oxidized and lost elasticity, the Gizzmo stem has a hairline fracture along its blow-molded seam, or internal thread tape was omitted during installation.
• Actionable Fix: Unthread the Gizzmo or remove the rubber plug. Inspect for structural cracks along the body. Apply 4 to 6 wraps of heavy-duty yellow PTFE thread tape to male Gizzmo threads. Re-insert the plug, spray the lip with a soap-and-water leak-detection solution, and verify zero micro-bubbles form under backpressure.

Scenario 2: Water Level in Pump Strainer Housing Keeps Rising Post-Blowout

• Root Cause: A failing main drain or skimmer diverter valve stem seal is allowing hydrostatic water pressure from the deep end to overcome the pad isolation setup, drawing water back up toward the equipment.
• Actionable Fix: Restart the air blower to re-evacuate the line. While air is actively purging, lubricate the valve stem seal with silicone grease and quickly turn the diverter valve past its stop point to verify positive closure. If the valve fails to seal, install an expandable rubber plug inside the pump housing intake port to create a double-seal barrier.

Scenario 3: Blower Motor Drops Output or Thermal Overload Trips

• Root Cause: Severe backpressure created by operating the blower against a fully closed valve manifold, or voltage drop caused by plugging the blower into an undersized (16-AWG) extension cord over 25 feet long.
• Actionable Fix: Immediately shut off power. Ensure at least one line (skimmer or return) is completely open before re-engaging the blower. Connect the blower directly to a dedicated 20-amp wall outlet, or use a heavy-duty 10-AWG or 12-AWG extension cord no longer than 50 feet.

Scenario 4: Air Escapes Through Waste Line During Return Purge

• Root Cause: The internal rubber spider gasket inside the filter multiport valve (MPV) is distorted, unseated, or missing a section, allowing air to bypass the return loop and vent through the waste port.
• Actionable Fix: Move the multiport valve handle through all positions to dislodge debris, then reset it firmly to "Recirculate." If air continues bypassing into the waste line, remove the top MPV cover screws, lift the diverter key assembly, and inspect or replace the damaged spider gasket using cyanoacrylate adhesive.

Frequently Asked Questions

Can I blow out my pool lines with a regular shop vacuum?

Standard shop vacuums can remove surface water from skimmer boxes, but most lack the air pressure (PSI) and continuous velocity needed to push water down deep suction lines or through long underground return loops. Vacuuming alone leaves pockets of water trapped in subterranean elbow joints that will freeze, expand, and rupture pipes.

What is the difference between propylene glycol and ethylene glycol antifreeze?

Propylene glycol is a non-toxic, eco-friendly fluid specifically engineered for pool plumbing and RV water systems. Ethylene glycol is automotive antifreeze, which is highly toxic to humans, pets, and aquatic plant life, and will damage pool surfaces and vinyl liners upon spring opening.

How do I know if the main drain line is properly air-locked?

A main drain line is correctly air-locked when you observe continuous, violent bubbling at the deep end pool grate while the blower is running, followed immediately by closing the main drain valve before turning the blower off. The sealed valve traps a compressed air bubble inside the vertical riser pipe that permanently holds water down below the frost line.

Do I need to pour antifreeze into return lines if they are fully blown out?

While not strictly required if a line is 100% dry, adding non-toxic propylene glycol acts as vital secondary insurance. If a rubber expansion plug degrades or shifts slightly over the winter, any ground moisture or melting snow entering the line will mix with the antifreeze solution, preventing it from forming a solid ice block.

Secure Your Pool Plumbing Against Freeze Damage

Properly executing a pool line blowout guarantees that your underground pipes, valves, and expensive equipment pad components survive sub-zero freeze cycles intact. If you lack high-volume blowers or encounter stubborn manifold leaks during winterization, consult a certified local pool service technician to safeguard your backyard investment before the first hard freeze hits.