Maintenance · 7 min read · July 2026

How to Blow Out Pool Lines

Water left in the plumbing freezes and cracks pipes. Clear your lines the right way — shop vac or compressor, expansion plugs, skimmer gizmo, and when antifreeze earns its place.

Contents
  1. 1. Why It Matters
  2. 2. What You Need
  3. 3. Step-by-Step
  4. 4. Pool Antifreeze
  5. 5. Mistakes
  6. 6. FAQ

Why Blowing Out Lines Matters

If you live where the ground freezes, this is the single most important part of closing a pool. Any water left sitting in the plumbing, pump, or filter can freeze, expand, and crack the pipe or the equipment housing — and a split underground line is an expensive dig-up repair. Blowing out the lines pushes that water out before winter can do the damage.

Timing matters: winterize once the water is reliably below about 65°F, but before hard freezes arrive — which is why this is peak-October work in most cold climates. Blowing lines is one step of a full close; the rest is in our closing guide.

What You Need

  • An air source — a shop vac switched to blower mode covers most residential pools; a dedicated air compressor gives more control. A household leaf blower can work in a pinch.
  • Expansion (winter) plugs for the return jets and a skimmer gizmo (or a bottle) for the skimmer — these seal lines and absorb any residual freeze.
  • Non-toxic pool antifreeze for lines you can't fully clear (never automotive antifreeze).
  • Basic tools to open drain plugs on the pump, filter, and heater.

Step-by-Step

  1. 1

    Lower the water below the skimmer and returns (per your closing routine), then shut off and drain the pump, filter, and heater via their drain plugs. Remove those plugs and keep them in the pump basket for spring.

  2. 2

    Set the filter valve appropriately and connect your air source at the pump or skimmer, depending on your plumbing. Blow air through each line in turn.

  3. 3

    For each return, blow air until you see steady bubbles at the jet in the pool, then plug it with an expansion plug while air is still flowing so it seats on an empty line.

  4. 4

    Clear the skimmer line, then seal it with a gizmo (or a partly filled bottle) that gives ice somewhere to expand without cracking the skimmer.

  5. 5

    Leave the equipment drain plugs out all winter, and store the pump indoors if you can. Any low spot that might hold water gets a splash of pool antifreeze.

When to Use Pool Antifreeze

Air handles most lines, but long runs, low spots, or plumbing you can't fully clear may hold a little water. Pouring non-toxic pool antifreeze into those lines protects them as backup. It's cheap insurance for underground runs you can't be sure are empty.

Never automotive antifreeze

Use only antifreeze labeled for swimming pools. Automotive (ethylene glycol) antifreeze is toxic and must never go into pool plumbing — it can contaminate the water it touches in spring.

This Is One Step of Closing

Blowing out lines fits into the full winterization routine — balancing, winter shock, cover, and equipment. The closing guide walks the whole sequence.

How to Close Your Pool

Common Mistakes

Leaving drain plugs in the equipment

A pump or filter with the plug still in can trap water and crack in the first hard freeze. Pull every plug and store them where you'll find them in spring.

Plugging returns after the air stops

If you stop the air before seating the plug, water flows back into the line. Plug each return while air is still bubbling so the line stays empty.

Waiting too long to close

Blow out the lines before the first hard freeze, not after. Once water in the pipes has frozen, the damage is already done.

FAQ

Do I need an air compressor to blow out pool lines?
No — a shop vac set to blower mode clears most residential pool lines and is what many owners use. A dedicated air compressor gives more pressure and control, which helps on long or deep plumbing runs, but it's not required. Whatever you use, the goal is steady airflow until you see bubbles at each return.
Can I skip blowing out lines if I use pool antifreeze?
Not really — antifreeze is a backup, not a replacement. Diluted by the water already in the line, antifreeze may not protect the whole run. Blow the lines out first to remove the bulk of the water, then use antifreeze on any low spot or line you can't be certain is clear.
When should I blow out my pool lines?
When the water is reliably below about 65°F but before any hard freeze — typically October in cold climates. Closing too early invites algae in still-warm water; closing too late risks a freeze cracking your pipes. Watch the forecast and aim for the window between the two.
Do I need to blow out lines if it doesn't freeze here?
No. Blowing out lines exists purely to prevent freeze damage. In a climate that stays above freezing, you can leave the plumbing full and run a lighter "winter" mode or keep the pool open year-round. This step is only for regions where the ground and pipes can freeze.