A suction-side air leak is the most common cause of a pump that won’t hold prime, a strainer pot that keeps filling with air, and a return jet that sputters water mixed with bubbles. The problem is that the leaks happen on the vacuum side of the plumbing — from the pool to the pump — so they don’t drip. You can’t see them. Here are three field-tested hacks that find air leaks fast, no special equipment required.
Hack #1: The shaving cream test
Grab a can of aerosol shaving cream from any drugstore. With the pump running and air actively being pulled into the system (visible bubbles in the strainer pot), shoot a generous bead of shaving cream around every suspect joint:
- The pump lid and lid o-ring perimeter
- Suction-side PVC unions (the threaded couplings between pipe sections)
- The pump body drain plugs
- The fittings where flexible hose meets PVC
If there’s a leak, the shaving cream gets sucked into the joint within 5–10 seconds — you’ll see a dent or pinhole open up in the foam. Vinegar, dish soap, or even water with a few drops of food coloring work too, but shaving cream is the most visible and clings best to vertical surfaces.
Hack #2: The lid o-ring water test
If the air is intermittent and you can’t find it with shaving cream, the lid o-ring is almost always the culprit. Turn the pump off, open the strainer lid, and fill the pot completely with water from the hose. Reinstall the lid hand-tight. Run the pump.
If the pump primes clean and holds, then drops prime again within an hour — you have a lid o-ring leak. The seal works briefly when the o-ring is freshly compressed but fails as it relaxes back into its old shape. Replace the o-ring. This is a $10 fix that solves more priming complaints than any other.
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Shop NowHack #3: The skimmer-line isolation test
If you have multiple suction sources (skimmer, main drain, vacuum line), one of them is leaking through a fitting underwater that you’ll never find from the equipment pad. Isolate each one.
The line that introduces air when isolated is your culprit. Most often it’s the skimmer — specifically a cracked weir door socket or a leaking thread sealant where the skimmer attaches to the suction pipe. Knowing which line lets you focus your pressure-test budget if you end up needing a leak detection service.
What about return-side leaks?
The plumbing between the filter and the return jets is on the pressure side, not the suction side. Leaks there drip visibly. If you see water on the pad, you have a pressure leak, not an air leak. Pressure leaks are usually easier to find — just look for the wet spot.
When to call for help
If you’ve worked through all three hacks and still have air, the leak is most likely underwater (cracked skimmer, leaking main drain pot) or buried (split underground PVC). At that point, a professional leak detection with a pressure tester and a microphone is faster than guessing. Reach out to PST Pool Supplies and we can help you find a local technician we trust.