How to Backwash a Sand Filter

In a sand filter, water flows into a multiport valve, down through a thick bed of filter sand, back up the multiport valve, then back to your pool via the return jets.

They require little maintenance besides replacing the sand about every 5 years and a backwash every week.

Even though it might not be the most effective form of filtration you can get, it’s certainly the easiest to take care of, so this type is the most common filter type in the UK.

Backwashing your sand filter is a very simple process which pushes all the debris and bacteria that it catches, out the waste line by using pool water reversed through the filter.

To backwash your swimming pool sand filter, you simply need to follow these steps.

Backwashing Your Pool

  1. Turn you pool pump OFF. And switch your multiport valve to “Backwash”
  2. Turn your pool pump ON and let water backwash your sand filter.
  3. Monitor the backwash water through the sight glass on the backwash line or from the top of the filter. When water is running clear (typicaly takes between 1-3 minutes) turn your pool pump OFF.
  4. Switch your multiport valve to “Rinse” and turn your pool pump ON
  5. Run the pump for 30 seconds to clear the filter and settle the sand back down. Then turn your pool pump OFF.
  6. Switch your multiport valve to “Filtration” and turn your pool pump ON.


A few points to note:

It is important to know what your filtration does with waste water before performing a backwash. If your water runs straight into a sewage system you are fine to perform a backwash without any problems or additional steps. If your water runs off to a soak away, then you need to be mindful of how much you backwash so as not to over saturate the area.

Never move the multiport valve with the pool pump on. Moving the valve with high pressure water running through it will likely cause the rubber gasket to come loose of break causing water to start running through your waste even when it is set to filtration.

The frequency of backwash is typically weekly however this is just a guideline. You should note the pressure of the sand filter (indicated by the pressure gauge typically located on the top of the filter. You should backwash your filter when the pressure reaches 10psi over normal running pressure.


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