How to Add Antifreeze to Pool Lines for Winter

Never use automotive coolant in your pool plumbing system

Automotive coolant and pool antifreeze look similar in a jug, but they are completely different chemicals. Car antifreeze contains ethylene glycol, an active ingredient that is highly toxic to humans, pets, and backyard wildlife. Pool antifreeze uses propylene glycol, which is non-toxic, biodegradable, and formulated specifically for recreational water systems and home plumbing. Pouring car coolant into your pool pipes creates a serious health hazard for anyone swimming in the pool when you reopen it in spring.

Ethylene glycol can also damage pool surfaces, staining vinyl liners and eating into plaster finishes. Propylene glycol, on the other hand, breaks down naturally and will not destroy your equipment or pool walls. You will usually spot it on store shelves dyed bright pink, showing that it is safe for drinking water lines, recreational vehicles, and swimming pools. Check the jug label carefully before you buy, and verify that it clearly lists propylene glycol as the primary ingredient.

Water expands by roughly nine percent as it freezes into solid ice. In a closed underground PVC pipe, that expanding ice builds thousands of pounds of outward pressure, splitting pipe walls and shattering elbows. Propylene glycol prevents this damage by changing how liquid freezes. Rather than freezing into a hard, rigid block, pool antifreeze turns into a soft, slushy gel that does not expand or split rigid plastic walls.

Before you introduce any chemical into your lines, inspect your skimmer housing for physical damage. If you notice cracks around the plastic throat where water drops lower than normal during the season, learn how to fix a pool skimmer leak without draining it so your winter chemicals stay inside the plumbing rather than seeping away into the surrounding soil.

Blowing out water protects underground pipes better than fluid

Pouring antifreeze straight into water-filled pipes without blowing them out first is one of the most common mistakes pool owners make. Underground swimming pool lines are rarely completely level. They dip and rise across the yard, creating low spots where water naturally gathers. If you pour liquid antifreeze into a pipe that is still filled with pool water, the chemical dilutes immediately. Diluted antifreeze loses its freeze protection, and that weakened mixture will freeze solid during a hard frost.

Forced air is your primary defense against winter freeze damage, while pool antifreeze serves as secondary insurance. Using forced air to clear the lines means connecting a commercial pool blower or a powerful wet-dry vacuum to the plumbing system at your equipment pad. The rushing air pushes standing water through the underground pipes and forces it out through the skimmer throats and wall jets. Once the bulk of the water is cleared from the lines, you create a dry air pocket that eliminates the main freezing hazard.

Adding antifreeze after clearing the lines protects the low bellies where forced air might leave tiny puddles behind. Even the strongest air blower can leave a thin stream of moisture along the bottom curve of an underground PVC run. Pouring undiluted propylene glycol into those cleared lines settles straight into those low spots. It mixes with the minor condensation or leftover moisture, keeping the mixture strong enough to survive sub-zero temperatures.

Above-ground pools are much simpler to manage because their plumbing lines are short and sit above the lawn. You can often disconnect flexible hoses, drain them dry by hand, and store them indoors for the winter. Inground pools, however, have long runs of rigid pipe buried under concrete decking and frozen dirt. A cracked underground pipe often means tearing up the deck with heavy equipment, making an air blowout paired with antifreeze worth every minute of preparation.

Follow these steps to add antifreeze to your pipes

1. Lower the pool water below the plumbing openings. Drain your pool water so the surface sits about 4 to 6 inches below the bottom of your skimmer mouth and below your wall return jets. This step prevents pool water from washing back into the lines while you work on them. If you use a heavy solid winter cover or live in an area with heavy winter rains, lowering the water level gives you room for seasonal precipitation without flooding the skimmer throat.
2. Drain all water from the pool equipment pad. Switch off all power to your pump, filter, and heater at the main breaker box. Remove the drain plugs from your pump strainer pot, the bottom of your filter tank, the chlorinator, and the heater header. Open the air relief valve on top of your filter tank to let air enter, which allows trapped water to pour freely out of the equipment. Store all small drain plugs inside your empty pump strainer basket so you do not misplace them over the winter.
3. Blow out the lines with forced air. Connect your blower hose to the pump inlet port or through the skimmer opening, depending on your setup. Turn on the blower to push standing water through the pipes until you see air bubbling vigorously out of the wall return jets and skimmer ports inside the pool basin. Keep the blower running until the bubbling stream turns into a fine, spitting mist, which confirms that the heavy water has exited the lines.
4. Add antifreeze to the skimmer lines. Look down into the bottom of your skimmer throat. You will usually see two threaded holes. The hole closest to the pool wall is often capped or connects to the main drain, while the hole farther back leads straight to your pool pump suction. Insert a funnel with a flexible hose extension into the suction pipe opening. Pour your undiluted pink pool antifreeze slowly through the funnel until you see the fluid resting inside the line.
5. Add antifreeze to the wall return lines. Wall return lines are the pipes that push clean, filtered water back to the pool basin. You can pour antifreeze into these pipes from the equipment pad by using a funnel placed directly into the pipe union after disconnecting your pool filter. Pour the fluid down into the line until it fills the low drop leading toward the pool wall. Alternatively, insert a flexible vinyl tube deep into the wall jet opening inside the pool, hold a funnel above the pool wall, and pour the antifreeze directly into the pipe opening.
6. Treat dedicated vacuum or suction cleaner lines. If your pool features an extra wall suction port designed for a suction-side cleaner, treat this pipe just like a skimmer line. Blow the line free of standing water, guide your funnel tube into the wall port, and pour your antifreeze into the line. Dedicated vacuum lines often feature narrow internal turns, so pour the fluid slowly to prevent it from splashing back out of the port onto your pool deck.
7. Protect the deep main drain pipe. The main drain sits at the deepest point of your pool floor, well below the natural frost line of the soil. Because you cannot easily pour liquid antifreeze into a drain pipe that sits submerged under several feet of water, protect this line using the air-lock method. Blow forced air from the equipment pad down toward the main drain until massive bubbles erupt at the pool bottom. While the air is bubbling, quickly close the suction valve at the pump pad to lock that air column inside the pipe, preventing water from rising back up toward the freezing surface.

Pour the right amount of antifreeze into each line

Using the proper volume of antifreeze ensures that residual water does not weaken the solution below its protective limit. Use this quick checklist to measure out your supplies before you begin closing your pool:

• Skimmer suction lines: Add 1 to 2 gallons of antifreeze per skimmer. Short plumbing runs close to the equipment pad only need 1 gallon, while skimmers located on the far side of a large yard require 2 gallons to protect the extra pipe length.
• Wall return lines: Add 1 to 2 gallons per return line run. If multiple return jets share a single manifold pipe coming from the equipment pad, pour 2 to 3 gallons total down through the pad connection to coat the shared pipe and branches.
• Dedicated vacuum cleaner lines: Add 1 gallon of antifreeze directly into the wall suction port using a flexible tube.
• Skimmer housing throat: Keep about half a gallon of fluid inside the skimmer basket area above the plug to keep any rainwater that enters from turning into a solid ice block inside the plastic bucket.

Weather conditions and geography play an important role in how much fluid you should use. If you live in an area where winter temperatures stay below zero for weeks at a time, the frost line can penetrate three or four feet into the soil. In those cold zones, use 2 full gallons in every plumbing run. In southern regions where winter frosts are brief and rarely freeze deep soil, 1 gallon per run provides plenty of defense against surface snaps.

Never add water to pool antifreeze to make a jug go farther. The liquid inside the jug is pre-blended by the manufacturer to provide a specific level of burst protection, often down to -50 or -100 degrees Fahrenheit. Adding tap water weakens that chemical balance instantly. Pour the fluid straight from the container into the pipe so it maintains its full protective strength against heavy ice.

Seal pipe openings with rubber expansion plugs and guards

Adding antifreeze does no good if pool water creeps back into the pipes while the pool sits idle. Once you have cleared the lines and poured your fluid, you must seal every opening tightly. Winter plugs block pool water from re-entering the plumbing from the pool side, keeping your lines dry and your antifreeze contained.

Rubber expansion plugs are the standard tool for smooth pipe openings and wall fittings. These plugs consist of a thick rubber cylinder sandwiched between two metal washers and fitted with a stainless steel bolt and wing nut. You press the rubber plug directly into the open pipe until it sits flush against the rim, then spin the wing nut clockwise. As the nut tightens, the metal washers squeeze together, forcing the heavy rubber to expand outward against the inside walls of the PVC pipe to form an airtight seal.

Threaded plastic winter plugs work best for fittings that feature internal threads, such as standard return wall jets after you unscrew the directional eyeball nozzles. These plugs include an integrated rubber O-ring around the base of the threads. Wrap a layer of pipe thread tape around the plastic threads, screw the plug into the wall fitting by hand, and snug it down with a pair of pliers until the O-ring compresses flat against the faceplate. This tight seal keeps groundwater and pool water from slipping past the threads during winter freezes.

Leaving winter lines improperly sealed can crack the pool shell itself as frozen soil shifts around the fittings. If freeze damage creates structural issues in your basin wall, you will need to understand how to repair cracks in a concrete pool without draining it before filling the pool back up for warm weather swimming. Protecting your pipe openings correctly eliminates that costly structural risk.

Your skimmer housing also needs crush protection from above. Even with a rubber plug threaded into the bottom hole, melting snow and rainwater will wash into the open skimmer bucket over the winter. As that trapped surface water freezes, it expands outward, crushing the brittle plastic skimmer walls. Screw a hollow plastic winter tube or freeze guard bottle into the bottom skimmer hole. When ice forms inside the skimmer bucket, it compresses the hollow plastic tube instead of cracking the skimmer body.

Flush out antifreeze before swimming when opening in spring

When warm weather returns and you are ready to open your pool, you must flush the lines before turning on your regular filtration cycle. Although propylene glycol is non-toxic and biodegradable, discharging several gallons of pink fluid straight into your pool will consume your free chlorine and turn clear water cloudy. Clearing the antifreeze out of your plumbing takes only a few minutes during spring startup.

• Unseal the pool openings: Remove the winter freeze tubes from your skimmers and unscrew the rubber expansion plugs and threaded caps from your return jets and cleaner lines.
• Vacuum excess fluid from the skimmers: Lower the hose of a wet-dry vacuum into the bottom of each skimmer throat. Suck out any pooled antifreeze and dirty melted snow sitting in the basin before opening the line down to the pump.
• Reinstall equipment pad plugs: Thread the drain plugs back into your pool pump pot, filter tank, and heater header. Lubricate the rubber pump lid O-ring with pool-grade silicone lubricant and secure the lid in place.
• Set the filter valve to waste: Rotate your multi-port filter valve handle to the "Waste" setting. This position routes incoming water directly out through your backwash discharge hose rather than running it through your clean sand, cartridge, or diatomaceous earth filter media.
• Blow out the lines with pump water: Prime your pool pump with water, open the skimmer and return suction valves, and switch on the power. Let the pump draw water through the plumbing runs for about 60 to 90 seconds. The rushing pool water will flush the pink antifreeze out through your waste hose.
• Resume normal filtration: Once clear water flows through the waste sight glass, switch off the pump. Turn the valve back to the standard "Filter" setting, restart the pump, and measure your chlorine, pH, and alkalinity levels using a reliable water testing kit.

Choose durable winter plugs and non-toxic pool antifreeze

Selecting the right winterizing supplies protects your swimming pool plumbing from freezing without introducing harsh chemicals into the water. Look for waterline antifreeze made exclusively with non-toxic propylene glycol. Avoid any product labeled as automotive coolant or containing ethylene glycol, as those chemicals are hazardous to swimmers and pets. Check the label for a sub-zero burst protection rating that matches your local winter conditions, with formulas rated to -50 or -100 degrees Fahrenheit offering the best defense for buried PVC lines.

When selecting winter plugs, check the exact diameter and thread style of your pipe openings. Most standard in-ground skimmers and return lines use 1.5-inch or 2-inch pipe fittings, while specialized cleaner ports and spa jets may require smaller plugs. Choose expansion plugs built with heavy-duty rubber and stainless steel bolts that resist rust from seasonal moisture. For threaded wall fittings, choose durable plastic plugs fitted with flexible rubber O-rings that will not slip or shrink when temperatures drop below freezing.

1

Garden at Home RV/Waterline Antifreeze RVs, Pools, Boats and Seasonal

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  9.2
• Brand
  Garden at Home

Key specs2

Burst Protection Rating

-100 degrees Fahrenheit rating

Plumbing Material Safety

Safe for rubber gaskets, rigid plastic PVC lines, elastomers, and metal fittings found across inground pool return lines and skimmer plumbing.

Pros & cons32

Pros

• Rated down to -100 degrees Fahrenheit to prevent severe winter pipe bursts
• Safe for pool plumbing plastics, rubbers, elastomers, and metal components
• Formula is non-toxic for potable water systems and seasonal waterline winterizing

Cons

• One gallon volume requires buying multiple jugs for longer pool plumbing runs
• Unsuitable for gas or diesel engine cooling systems

2

XtremepowerUS 1.5"" Pool Plug Cap, Swimming Pool Return Line Winter

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  9.2
• Brand
  XtremepowerUS

Key specs2

Fitting Thread Compatibility

1.5-inch NPT male threaded connection

Freeze Resistance

Engineered from rigid composite material paired with a durable O-ring that resists shrinking and slipping in sub-zero winter pool water.

Pros & cons32

Pros

• Threaded 1.5-inch NPT male connection screws directly into return fittings
• Integrated O-ring creates a watertight seal without shrinking in freezing cold
• Prevents water from re-entering cleared return lines, skimmers, or cleaner pipes

Cons

• Only fits 1.5-inch threaded ports and cannot seal unthreaded smooth pipes
• Includes only a single plug per pack so multiple fittings require extra units

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IMPRESA 20-Pack of Pool Skimmer Socks - Excellent Savers for

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  9.0
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  IMPRESA

Key specs2

Basket Compatibility

Flexible elastic construction conforms to Hayward, Pentair, Intex, and Swimquip skimmer baskets for above ground and inground pools.

Maintenance Interval

Clean with hose and replace every 4 to 8 weeks

Pros & cons32

Pros

• Ultrafine nylon mesh catches fine debris, pollen, and hair before it enters pipes
• Elastic band stretches over virtually any skimmer basket shape or brand
• Value pack provides 20 reusable socks to protect filtration gear before closing

Cons

• Dissolving chlorine tablets in the basket can degrade and tear the nylon mesh
• Does not provide freeze protection or pipe sealing capability on its own

4

Aquatix Pro Pool Winterizing Plug Premium 1.5" to 2" Swimming

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  8.8
• Brand
  Aquatix Pro

Key specs2

Expansion Size Range

Fits 1.5-inch to 2-inch pipe openings

Hardware Construction

Combines a heavy-duty rubber compression sleeve with a stainless steel bolt to resist harsh pool chemicals and winter water corrosion.

Pros & cons32

Pros

• Expands from 1.5 inches to 2 inches to fit varying unthreaded plumbing ports
• Stainless steel bolt resists rust and corrosion across long winter exposure
• Heavy-duty rubber body compresses tightly to block skimmers and return jets

Cons

• Requires manual tightening of the bolt to achieve a leak-free expansion seal
• Single plug per package requires separate purchases for multiple pool lines

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SeaKlear AquaPill AP71 WinterPill Swimming Pool Winterizer Pill, Translucent Light

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  8.8
• Brand
  SeaKlear

Key specs2

Water Treatment Capacity

Treats up to 30,000 gallons

Release Duration

6-month continuous delivery system

Pros & cons32

Pros

• Treats up to 30000 gallons of pool water under the winter cover
• Patented 6-month slow-release delivery system maintains water quality all winter
• Safe for all pool interior surfaces and compatible with mesh safety covers

Cons

• Does not seal pool plumbing or protect underground pipes from freezing
• Pools over 30000 gallons require additional treatment units

6

Universal Tapered Rubber Winter Expansion Plug for Winterizing Pools or

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  8.4
• Brand
  American Granby

Key specs2

Small Line Sizing

Fits 0.5-inch to 1-inch pipe diameters

Fastening Hardware

Includes a stainless steel slotted screw, matching washer, and a nylon wing nut designed for manual tightening without hand tools.

Pros & cons32

Pros

• Tapered rubber plug seals smaller 0.5-inch to 1-inch plumbing and equipment lines
• Nylon wing nut allows quick hand-tightening without searching for specialized tools
• Stainless steel slotted screw and washer provide dependable corrosion resistance

Cons

• Too small for standard 1.5-inch or 2-inch pool skimmer and wall return lines
• Narrow pipe size range requires confirming exact internal pipe diameter first

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HTH 52038 Swimming Pool Care Green to Blue, Advanced Shock

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  8.2
• Brand
  HTH

Key specs2

Water Clearing Speed

Clears green pool water in 24 hours

System Requirements

Effective for all pool types that support vacuuming to waste, requiring a pool pump and multi-port valve with waste capability.

Pros & cons32

Pros

• Clears severe green algae blooms within 24 hours prior to winter closing
• Calcium hypochlorite formula avoids adding cyanuric acid or causing chlorine lock
• Flocculant settles suspended particles directly to the floor for vacuuming

Cons

• Requires a pool filtration setup capable of vacuuming directly to waste
• Does not replace winter pipe antifreeze, blowout plugs, or skimmer guards

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CMP Splash Skimmer Winter Tube with Plug 17.5in, In-Ground 25251-120-000

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  8.2
• Brand
  Horizon

Key specs2

Skimmer Freeze Protection

The 17.5-inch hollow tube compresses under ice pressure, preventing expanding frozen water inside the skimmer housing from cracking the plastic walls.

Skimmer Thread Sizing

Fits 1.5-inch to 2-inch internal threads

Pros & cons32

Pros

• Screws into 1.5-inch and 2-inch internal threads to seal inground skimmer ports
• Cylindrical 17.5-inch body compresses to absorb ice expansion inside the skimmer
• Easy-grip top allows tool-free installation and quick removal in the spring

Cons

• Built specifically for inground skimmers and unsuitable for above ground skimmer boxes
• Threaded base requires clean, undamaged skimmer threads to ensure a proper fit

9

Skimmer Vortex- The Easiest Solution to a Cleaner Pool. Built

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  7.0
• Brand
  Skimmer Vortex

Key specs2

Skimmer Basket Size

Built for 8-inch skimmer baskets

Operating Water Level

Designed to function most effectively when the pool water level sits 2 to 3 inches above the skimmer basket during the active swim season.

Pros & cons32

Pros

• Drops directly into 8-inch skimmer baskets with no assembly or tools required
• Helps optimize surface water vortex action during regular pool operating season
• Backed by durable American manufacturing and a lifetime guarantee

Cons

• Sized exclusively for 8-inch skimmer baskets and will not fit smaller units
• Operational cleaning accessory that provides no freeze protection during winter

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