How to Backwash a Pool Filter: Step-by-Step Guide (Sand and DE)

How Do You Backwash a Pool Filter?

To backwash a pool filter, turn the pump off, set the multiport valve to BACKWASH, and run the pump for 2 to 3 minutes until the sight glass runs clear. Turn the pump off again, set the valve to RINSE, and run for 30 to 60 seconds to re-settle the sand bed. Turn the pump off, return the valve to FILTER, and restart. Note the new pressure reading as your clean baseline.

1. Pump OFF. Never move the valve under pressure.
2. Valve to BACKWASH.
3. Pump ON for 2 to 3 minutes, until the sight glass runs clear.
4. Pump OFF.
5. Valve to RINSE, pump ON for 30 to 60 seconds, then pump OFF.
6. Valve back to FILTER, pump ON, and write down the new baseline PSI.

The whole cycle takes under 10 minutes. DE filters need one extra step afterwards: fresh DE powder through the skimmer. Cartridge filters have no backwash position at all.

The One Rule That Prevents Most Backwash Mistakes

Before anything else: always turn the pump off before moving the multiport valve.

Moving the valve while the pump runs cracks the valve body. It happens constantly, and it is a $150 to $300 fix that is 100% avoidable. Every step in this guide starts with the pump off.

What Backwashing Actually Does

Your filter traps debris in the sand or DE media as water flows downward from the inlet. Over time, the trapped debris increases resistance, and that is why pressure rises.

Backwashing reverses this flow: water comes in from the bottom, travels up through the media, and carries the trapped debris out the waste/backwash line. Think of it as flushing the filter in reverse.

The result: the debris is removed, pressure drops back to your clean baseline, and the filter resumes efficient operation.

Step-by-Step Backwash Procedure

Follow the steps in the How-To section above. Here is what each step looks like in practice:

The Sight Glass: Your Key Indicator

The sight glass is the small clear tube or viewport on the multiport valve. It shows you what the backwash water actually looks like.

When you start the backwash cycle, the sight glass will be dark and cloudy, and that is the debris. As backwashing continues, it gradually clears. Stop when it runs fully clear. Running the backwash longer than needed wastes water without additional benefit.

The RINSE Step: Do Not Skip This

RINSE is the step most pool owners skip, and it is why sand ends up in their pool after backwashing.

After backwashing, the sand bed is disturbed, and some sand is loosened and floating near the top of the tank. If you go straight from BACKWASH to FILTER, that loose sand returns through the laterals and into your pool via the return jets.

RINSE runs water in the normal filter direction for 30 to 60 seconds to re-settle the sand into a compact, level bed before returning to normal operation. For a full breakdown of every valve position and what each one does, see the pool filter valve settings guide.

How Long to Backwash and How Often

Two numbers cover almost every residential pool.

Duration: 2 to 3 minutes of backwash, then 30 to 60 seconds of rinse. The sight glass, not a stopwatch, tells you when to stop the backwash. Once the discharge runs clear, further running only sends clean water down the drain. If the water is still visibly dirty after 5 minutes, the sand is saturated with body oils and sunscreen, which a chemical filter clean removes and a backwash cannot.

Frequency: backwash when the pressure gauge reads 8 to 10 PSI above your clean baseline. That is the only trigger that matters.

Calendar schedules fail because filter loading has nothing to do with the day of the week. It tracks bather load, wind, pollen, and rainfall. A pool that hosted twelve swimmers on Saturday may hit the trigger by Sunday. The same pool unused through a cool week may sit at baseline for 3 weeks. Backwashing on a fixed Saturday routine means you are either running a clogged filter for days or flushing a filter that was still working well.

For the full breakdown of both numbers, see how often to backwash a pool filter and how long to backwash a pool filter.

Backwashing by Filter Type

The procedure above is the sand filter procedure. The other two media types differ, and one of them cannot be backwashed at all.

Sand filters. The standard multiport procedure: pump off, BACKWASH for 2 to 3 minutes, pump off, RINSE for 30 to 60 seconds, pump off, back to FILTER. Push-pull (slide) valves follow the same sequence with a plunger instead of a rotating handle, and they still require the pump off before you move it.

DE filters. Identical sequence, plus a mandatory recharge. Backwashing strips the diatomaceous earth off the grids, and bare grids barely filter. Immediately after returning to FILTER, add roughly 80% of the filter’s rated DE capacity as a slurry through the skimmer. Full procedure: how to backwash a DE filter.

Cartridge filters. These cannot be backwashed. There is no multiport valve and no reverse-flow path, so there is nothing to switch. If someone tells you to backwash a cartridge filter, they are describing the wrong system. The equivalent maintenance is opening the housing, lifting the cartridge out, and rinsing the pleats with a hose, then soaking in a filter cleaner once or twice a season. See can you backwash a cartridge filter and how to clean a cartridge pool filter.

Sand Filter vs DE Filter: One Important Difference

The backwash procedure is identical for sand and DE filters up through the RINSE step. The critical difference is what comes next for DE filters.

After every backwash of a DE filter, you must replenish the DE powder.

DE grids are just fabric frames. The diatomaceous earth powder coated on them is the actual filtering medium. Backwashing strips off most of that coating. Without fresh DE, the water flows through the bare grids and directly back to the pool, barely filtered at all.

After the RINSE cycle on a DE filter:

1. Calculate how much DE your filter needs (approximately 80% of the rated total capacity)
2. Mix DE powder with water in a bucket to form a slurry
3. With the pump running on FILTER, slowly pour the slurry into the skimmer
4. The DE will travel to the filter and coat the grids evenly

See our guide on how much DE for pool filter for exact quantities by filter size.

How Often Should You Backwash?

Backwash when your pressure gauge reads 8 to 10 PSI above your clean baseline, not on a weekly schedule.

Your clean baseline is the pressure reading immediately after a fresh backwash when your filter is working at full efficiency. For most residential filters, this is 8 to 12 PSI.

When that reading rises to 18 to 22 PSI (8 to 10 PSI above baseline), it is time to backwash.

Why does the calendar schedule fail? Because filter loading depends on bather load, weather, and seasonal factors, not the day of the week. After a summer pool party or a heavy rainstorm, you may need to backwash the next day. During a mild week with no use, you may go 3 weeks without a pressure rise.

Write your baseline PSI on a piece of waterproof tape and stick it on your filter housing.

If your gauge reads zero with the pump running or never moves between backwashes, it has failed. A 0 to 60 PSI pool filter pressure gauge costs a few dollars and screws straight into the filter head.

Backwashing Mistakes That Damage the Filter

Five mistakes account for nearly every backwash-related repair bill.

1. Turning the multiport valve while the pump is running. The spring-loaded diverter inside the valve is sealed against the port faces by system pressure. Rotating it under load shreds the spider gasket and can crack the valve body outright. The gasket alone is a fiddly repair; a cracked body means a new valve. Pump off, every single time.

2. Skipping RINSE. Straight from BACKWASH to FILTER sends the loosened top layer of sand out through the laterals and into the pool, where it settles on the floor and gets vacuumed right back into the system. Thirty to sixty seconds on RINSE prevents it.

3. Backwashing far too often. A lightly loaded filter traps finer particles than a freshly cleaned one, because the debris cake itself acts as a filter medium. Backwashing every week on principle strips that cake before it does any work, and each cycle sends 200 to 500 gallons of treated, heated, chemically balanced water down the waste line. You then refill and rebalance it.

4. Backwashing instead of an annual chemical clean. Backwashing removes loose debris. It does nothing about the body oils, sunscreen, and lotions that bind to the sand grains and turn the top few inches into a greasy crust. When your post-backwash baseline pressure creeps upward season over season, that crust is the reason. A filter cleaner soak once a year fixes what no amount of backwashing will.

5. Ignoring where the waste water goes. Backwash discharge is chlorinated and often high in stabiliser and metals. Dumped at the equipment pad it kills plants, saturates the ground next to the foundation, and in many municipalities it is illegal to send it into a storm drain. Run a proper backwash hose to an approved discharge point and check your local rules before the first cycle of the season.

Related Guides

• How Often to Backwash Pool Filter: the PSI method explained in detail
• How to Backwash a Hayward Pool Filter: model-specific steps
• How to Backwash a DE Filter: DE-specific procedure
• How to Change Pool Filter Sand: when backwashing stops working