Short answer
Backwash when the pressure gauge reads 6 to 8 psi above your clean reading (Hayward’s figure; Inyo Pools says about 10). With the pump off, set the valve to BACKWASH, run the pump about 2 minutes or until the sight glass runs clear, turn it off, set RINSE for 30 seconds to a minute, then back to FILTER. Always turn the pump off before moving the valve handle.
When to backwash
Right after the sand is fresh or freshly backwashed, read the gauge with the pump running and write it down: that is your clean pressure. It varies from pool to pool. Hayward’s manual says to backwash when the gauge is 6 to 8 psi (0.41 to 0.55 bar) higher than that. Inyo Pools uses about 10 psi for the Pentair Triton II. Follow your own filter’s manual where it gives a figure.
How to backwash, step by step
Turn the pump off
Never move the multiport handle with the pump running. It can damage the valve’s spider gasket.
Roll out the backwash hose
Connect a backwash hose to the waste port if you use one, and route it where the water can drain legally and safely.
Set the valve to BACKWASH
Press the handle down and turn it to BACKWASH.
Run the pump
Start the pump and watch the sight glass or the hose. The water runs cloudy, then clears. Hayward says about 2 minutes or less.
Turn the pump off
Stop the pump before you touch the handle again.
Set RINSE and run it briefly
Turn to RINSE and run the pump for about 30 seconds to a minute. This resettles the bed and sends the leftover dirty water to waste.
Back to FILTER
Pump off, set FILTER, start the pump, and check that the gauge is back near your clean reading. Top up the pool if the level dropped.
What each valve position does
Backwash and rinse are two of six settings on most multiport valves. Waste, recirculate and closed have their own jobs: see sand filter valve settings.
Troubleshooting
| Problem | Likely cause | What to do |
|---|---|---|
| Sand in the backwash water | Fines after a fresh fill, or a cracked lateral | A little after a fill is normal; lots, or sand in the pool, needs a check |
| Pressure stays high after backwash | Oily or caked sand, closed return, stuck gauge | Check valves, swap the gauge, consider fresh sand |
| Backwash needed every few days | Algae, heavy debris, or worn sand | Clear the water first; if it persists, see how often to change sand |
| Water leaks from waste line in FILTER mode | Worn spider gasket in the valve | Replace the gasket or the valve |
More causes in Leslie’s troubleshooting guide, and in our guides to sand in the pool and when to change the sand.
What you need
Questions people ask
How often should I backwash my sand filter?
By pressure, not by calendar. Note the gauge reading when the sand is clean, and backwash when it rises 6 to 8 psi above that. After algae, heavy storms or a big opening clean-up you may need to backwash more often for a while.
How long should I backwash a sand filter?
Hayward says about 2 minutes or less, depending on how dirty the filter is, until the water in the sight glass is clear. Running it much longer mostly wastes water.
Why do I need to rinse after backwashing?
Rinse resettles the sand bed and flushes the dirty water left in the tank out to waste instead of back into the pool. Hayward says to run rinse for about 1/2 to 1 minute.
Can I backwash too much?
Backwashing more often than the pressure calls for sends pool water to waste and adds wear on the valve for no gain. Wait for the 6 to 8 psi rise.
Why does my pressure stay high after backwashing?
The sand may be bound with oils and scale, the return line may be partly closed, or the gauge may be stuck. If clean pressure keeps creeping up season to season, the sand may be due for replacement.
Sources
Last reviewed October 12, 2026. Sand amounts and listings change; check your filter’s label or manual before you buy, and follow the maker’s instructions.