How to Blow Out Pool Lines for Winter

Choosing Safe Air Equipment for Your Pool Pipes

Water expands by roughly nine percent when it freezes solid. When trapped water freezes inside rigid underground PVC pipes, the ice pushes outward until the plastic splits along the seam. Pushing that trapped water out before winter hits requires the right kind of air tool. Many pool owners assume they need intense air pressure to clear long plumbing runs, but the opposite is true. You need a large volume of moving air rather than high pressure to empty pool plumbing safely.

Air tools operate on two main factors: CFM (volume of moving air, measured in cubic feet per minute) and PSI (air pressure level, measured in pounds per square inch). Underground pool pipes are wide, usually 1.5 inches to 2 inches in diameter. To clear them, you need an air source that produces enough CFM to push an entire column of water forward like a solid piston. A dedicated commercial pool blower pushes over 100 CFM at a gentle pressure of 2 to 4 PSI, which empties pipes quickly without straining plastic pipe joints.

A wet-dry shop vac can work on many inground pools if you use the exhaust blower port instead of the suction port. The vacuum needs a motor rating of at least 5.0 to 6.5 peak horsepower to generate enough volume to move deep water columns. A weaker shop vac will simply hum while the water column pushes back against the air flow. If your pool has long pipe runs or deep plumbing lines, a basic household vacuum may struggle to break the initial water barrier.

A standard home air compressor works very differently. Compressors produce high PSI, often 90 to 120 PSI, but very low air volume, usually just 3 to 6 CFM. Pumping high-pressure air through rigid pool plumbing is dangerous. High pressure can rupture buried PVC glue joints, crack thin plastic valve bodies, or turn a rubber winter plug into a dangerous projectile. If you choose to use an air compressor, you must install an adjustable pressure regulator, set the dial firmly below 20 PSI, and confirm the pressure never climbs higher while lines are closed.

Prepping Your Equipment Pad and Pool Valves

Before you attach an air source, you must prepare the equipment pad so air can travel freely through your pipes. Trapping air behind closed valves or pressurized filter tanks creates a major safety hazard. Always turn off the electrical power to your pool pump, booster pump, and heater at the main breaker panel before loosening any fittings. Never rely on an automated timer or an app to keep the equipment turned off while you work.

Draining the water from your above-ground pool equipment comes next. Air cannot push water out of underground lines if it has to fight through a pump basket or filter tank full of standing water. Walk around your equipment pad with a bucket and wrench to empty every component in order.

• Remove the two threaded drain plugs from the pump housing (one on the front wet end and one underneath the strainer pot) and let the water pour out.
• Unscrew the drain cap at the bottom base of the filter tank and open the manual air relief valve on top of the filter tank to release internal suction.
• Take out the winter drain plugs from your pool heater header to protect its delicate internal copper heat exchanger from freezing.
• Turn the multiport valve (the handle on top of or next to the filter that routes water) to the "Winterize" position, or park the handle directly between two labeled detent notches so the internal rubber gasket is not pinched tight.
• Unscrew all directional eyeball fittings from the wall return lines inside the pool so water can exit without restriction.

Once the equipment pad is completely drained, leave the small equipment drain plugs inside the open pump strainer basket for safe keeping over the winter. Setting the multiport valve to the winter position opens all internal ports at once. This prevents trapped water from cracking the valve body while you send air through the plumbing system.

Step-by-Step Guide to Blowing Out Skimmers and Return Lines

The standard connection point for blowing out pool lines is the pump strainer basket. You can attach your air blower hose directly to the pump intake using a threaded blowout adapter or a tapered rubber cone fitting. Always blow out the suction lines first, then move to the pressure lines. Suction lines sit higher in the ground and run straight to the skimmer, making them easier to clear before you direct air into the longer return runs.

1. Connect the air source to the pump intake. Clamp your blower hose into the front port of the pump housing, which leads straight out toward the skimmers and main drain. If you use an air compressor with an adapter, screw the adapter into one of the pump housing drain plug holes.
2. Direct air to the skimmer line. Adjust your intake valves at the equipment pad so the main drain line is closed and the skimmer line is completely open. Turn on your blower. Air will push water through the underground pipe toward the skimmer opening in the pool wall.
3. Watch for water discharge. Within thirty to sixty seconds, a heavy geyser of water will shoot out of the bottom port inside the skimmer well. Let the air run until the water stream breaks into a light, spitting mist, followed by a loud rush of pure air.
4. Seal the skimmer under air pressure. While the blower is running and air is actively hissing out of the skimmer hole, install a rubber expansion plug or screw in a winter protection tube. Sealing the line while air pushes outward guarantees that pool water cannot back-siphon into the cleared pipe.
5. Switch the valves to clear the return lines. Turn off the blower, move your air hose connection to the discharge side of the pump or directly into the filter multiport valve, and set the valve to "Recirculate." Turn the valve handles so air routes toward the return lines (the wall jets pushing filtered water back to the pool).
6. Blow out the wall jets in sequence. Turn on the air source. Water will begin bubbling violently from the return wall jets. Always plug the jet closest to the equipment pad first as soon as it blows pure air. Sealing the closest jet forces the full volume of moving air to the next jet down the line until every return is completely clear and plugged.
7. Clear the dedicated cleaner line. If your pool features a dedicated vacuum wall port for a suction cleaner or pressure cleaner, open its specific valve and let air blow through until the water clears. Thread a solid winter plug with a rubber O-ring into the wall fitting while air continues to bubble out.

Take your time on each pipe run. If you plug a wall jet too soon while water is still surging out in heavy bursts, you leave gallons of water trapped in low dips beneath the ground. Let the air hiss cleanly for at least twenty seconds after the last water spray before tightening down your winter plugs.

How to Air-Lock the Main Drain Without Diving

The main drain sits at the deepest point of your pool floor, often six to eight feet underwater. Swimming down to the bottom of a freezing pool to screw a plug into the main drain cover is difficult and dangerous. Fortunately, you do not need to install a physical plug in the bottom drain to protect the plumbing line from freeze damage.

The frost line in most cold regions penetrates between eighteen inches and three feet into the soil. Because the bottom drain pipe sits deep underground beneath thousands of gallons of insulating pool water, the lower section of that pipe will not freeze. The danger zone is the vertical pipe section that climbs out of the ground near the equipment pad. You protect this pipe by creating an air lock.

To create an air lock, attach your blower to the pump intake and set your equipment pad valves so all skimmers are closed and only the main drain line is wide open. Turn on the blower. The air will slowly force the heavy column of water down the pipe toward the bottom of the pool. Because pushing water eight feet down against water pressure takes real effort, you may need to wait one to two minutes before you see results.

Watch the surface of the pool directly above the deep end. You will see massive, rolling air bubbles break across the surface as air clears the drain grates. Let the air boil violently for roughly thirty seconds to verify that water has been pushed deep below the frost line. While the blower is running at full power and air is still bubbling up from the floor, quickly turn the main drain valve handle completely closed. Turn off your air blower immediately after closing the valve.

Closing the valve while air is flowing traps the pressurized air pocket inside the pipe. This works like turning an empty drinking glass upside down and pushing it underwater into a sink. The trapped air bubble cannot escape, so water cannot rise back up into the shallow, vulnerable section of the pipe near the surface.

Sealing Pipes and Protecting Skimmers with Antifreeze

Once every underground pipe is cleared of water, your plugs and sealants serve as the final barrier against winter damage. Rubber expansion plugs (rubber cylinders that expand when you turn a metal wing nut) work well in smooth PVC fittings. Threaded plastic plugs wrapped with several layers of Teflon tape work best in threaded jet openings. Check each rubber plug before installing it to confirm the rubber is soft, supple, and free of cracks.

Skimmers need special protection because they sit right at the freezing waterline. Rain, melting snow, and surface ice will naturally enter the skimmer well over the winter. As water freezes inside the rigid plastic box, it expands outward, which can crack the skimmer walls and cause massive underground leaks. You must install a Gizzmo (a hollow plastic tube screwed into a skimmer to absorb ice squeeze) directly into the bottom port of the skimmer.

A Gizzmo features flexible, thin plastic walls. When surface water freezes inside the skimmer, the expanding ice crushes the hollow tube instead of breaking the skimmer housing. Wrap the threads of the Gizzmo with Teflon tape before screwing it into the cleared bottom hole of the skimmer. If you do not have a Gizzmo, thread a solid rubber plug into the hole and place an empty, sealed plastic antifreeze jug partially filled with small stones into the skimmer basket to absorb the ice crush.

Adding non-toxic pool antifreeze gives your plumbing an extra safety net. Use only non-toxic propylene glycol antifreeze designed specifically for swimming pools or recreational vehicles. Never use automotive antifreeze (ethylene glycol), which is extremely toxic to pets, wildlife, and pool liners. Pour roughly one gallon of pool antifreeze down each skimmer pipe before installing your final plug or Gizzmo. If a small trickle of rain water slips past a plug during a mid-winter thaw, the antifreeze prevents that water from turning into solid ice.

Taking the time to blow out and seal every line properly saves you thousands of dollars in emergency concrete excavation repairs. You will appreciate that extra effort when learning how to open an inground pool safely next spring, because your pump will prime quickly and every underground pipe will hold pressure without leaking.

FAQs

Can a standard wet-dry shop vac blow out deep pool lines?

A shop vac can clear shallow skimmer pipes and short return runs if it has an exhaust blower port and a motor rated at 5.0 peak horsepower or higher. However, standard shop vacs often struggle to clear deep main drains or long pipe runs because they lack the continuous air volume needed to push deep water columns. For deep inground pools, a high-volume commercial pool blower produces much better results.

What air pressure level will damage underground PVC pipes?

Air pressure levels above 20 to 25 PSI can easily crack aging PVC fittings, break valve housings, or blow glued pipe joints apart underground. When using an air compressor, always attach a dedicated pressure regulator, dial the output down to roughly 10 to 15 PSI, and keep lines open so air pressure never builds up inside closed pipes.

Do I still need pool antifreeze if I blow all the water out?

Antifreeze is not strictly mandatory if every drop of water is removed, but it serves as an inexpensive insurance policy against freeze damage. Water from heavy winter rains or melting snow can slowly leak past worn rubber plugs over several months. Adding one gallon of non-toxic pool antifreeze to each skimmer line guarantees that any small leaks will not freeze solid and crack your pipes.