Pool Filter Backwash Valves

Pool Filter Backwash Valves

On very early pool filters, there were no single motion backwash valves, you had to turn several gate valves to reverse the flow through the filter. Or you just drained and cleaned your DE filter septums.

The backwash valve, either a push pull or multiport valve attached to the filter, was introduced to switch the water direction in one easy movement. As the backwash water leaves the tank, the dirty water is released out of the waste port of the valve, which may be connected to a pipe or discharge hose.

What is Backwashing?

Cleaning a Sand or DE pool filter. Backwashing involves sending the water backwards through the filter, to flush out the dirt that is trapped inside the filter sand bed, or to flush out dirty DE filter powder. Cartridge filters are not backwashed, only Sand and DE pool filters. Cartridge filters are removed for cleaning, and are therefore not equipped with backwash valves.

How Long do I Backwash a Pool Filter?

Backwash until the water runs clear out the waste line, normally about 2 - 3 minutes. You may need to add water to the pool before or after backwashing. Many valves have a backwash sight glass that you can view the water during backwashing, or you can look at the end of the hose, to see when it starts to run clear, indicating that backwashing is complete.

For D.E. filters, backwashing several times will remove more dirt and DE. For example, backwash for 2 mins, filter for 10 secs, Backwash for 1 min, filter for 10 secs, Backwash for 30 seconds, then back to filter, always shutting off the pump before moving the filter valve. This ‘bumping’ process removes more DE powder than just a single backwashing. On a D.E. filter, the last step is to add the fresh DE powder or Perlite to the filter, through the skimmer, to replace what was flushed out. Add 4 cups (32 oz) of D.E. for each 10 sq ft of filter surface area. Because DE powder has twice the volume, 1 lb of DE is actually 32 oz. of dry measure.

Be careful during backwashing to move the discharge hose as needed to avoid oversaturation or erosion, or flooding of downhill neighbors (human or animal). DE powder can damage lawns and harm streams, so be especially cautious of where the discharge is flowing. Pool chemical levels should be normal and water balanced before discharging water. Your local authorities may have specific restrictions on pool discharge and draining. You can capture and dispose of DE powder by using a separation tank on the backwash line, or by attaching a Slime Bag to the end of your backwash hose.

How do I Backwash a pool filter?

  1. Shut off pump, roll out backwash hose, check waste line for any closed valves.
  2. Turn multiport valve handle to backwash, or slide a push pull valve.
  3. Turn on pump. Water should flow out backwash pipe or hose.
  4. Backwash until water runs clear, about 2-3 minutes.
  5. Shut off pump, turn valve back to filter, turn filter back on.
  6. Note lower pressure on filter tank, and increased flow rate.


The Push-Pull valve, also called a Slide valve, mounts to bulkhead fittings on the side of a Sand or D.E. filter. The advantages of a Push-Pull valve are that they are simple to use, simple to understand, have very few parts, and are less restrictive to water flow than the multi-port valve. Because of this high flow, low pressure advantage, Slide valves have gained a new popularity among variable speed pump owners, looking to gain more energy savings from their investment.

Push-Pull Valves use a plunger with two disks attached, and a handle at the top of the piston. The only action is to either pull the handle up, or push the handle down. Sand filters usually operate in filter mode with the plunger in the up position, and backwash by pushing the handle down (always shut off pump before changing a backwash valve). D.E. filters are usually in filter mode when the plunger is down, and backwash by pulling up on the handle. Keep that in mind, if converting from a Multiport to a Slide valve.

When you pull up or push down on the plunger (aka piston) of a push pull valve, you are reversing the direction of water into and out of the filter. This is where we get the word "back-wash", because we are sending the water through the filter backwards, to flush out trapped dirt.

Slide Valve Maintenance

Lubricate the valve o-rings every opening and closing of each season. Remove the plunger from the valve body and apply a Teflon based lubricant like [Magic Lube(https://intheswim.com/p/magic-lube-ptfe-blue-label---1-oz./324789.html) to all disk and cap o-rings. Replace the plunger o-rings every 5 years, or as needed. Keeping an extra set of plunger piston o-rings on-hand, can get you back in action fast, if you should 'blow a gasket' during a backwash operation.

Slide Valve Leaking Water

If you are leaking water out of the waste line or backwash line, while in the filter position, the bottom plunger o-ring may have slipped off. You may find it at the end of the backwash hose, out in the yard.

And if you are missing the middle or upper o-ring on the plunger, this can cause some water to bypass the filter during both filter and backwash modes. You may also experience leaking up through the lid, around the plunger rod. Beneath the cap are 1 or 2 small o-rings on the shaft where it runs through the lid or cap.

Remove the plunger from the valve body and inspect for broken or missing plunger o-rings, and replace as needed. Lubricate with Silicone lubricant, or replace the o-rings to seal up a leak. Might be a good time to replace all valve o-rings with our pool filter Valve Rebuild Kits.

multi-port valves

The multiport valve, sometimes abbreviated as MPV valves, mounts onto bulkhead fittings on the side of a Sand or D.E. pool filter. Many sand filters use a top mounted multiport valve, located on the top center of the filter tank. The main advantage of a Multiport valve is that they have multiple ports, for more functions than simply Filter or Backwash. The disadvantage of multiport, as compared to a push-pull valve, is that they are more complicated to understand and repair, and have many more valve parts, with a greater potential for internal problems.

Multiport valves usually have 6 positions (Some Jacuzzi valves have 7 and some American valves have 8). The positions are usually labeled: Filter, Backwash, Rinse, Recirculate, Closed and Drain/Waste. These are described below in more detail.

When you move the multiport valve from Filter to Backwash, (always shut pump off first) you are reversing the direction of water into and out of the filter. This is where we get the word "back-wash", from sending the water backwards thru the pool filter tank to wash out trapped dirt and debris.

multiport valve maintenance

There really is no maintenance on a MPV. Just make sure to winterize properly if you are in the snowbelt. They don’t require any lubrication or calibration. Replacing the gaskets and o-rings every 10 years could be wise, or just wait until it is demanded.

The most common multiport valves and push-pull valves have Go-Kits, aka Valve Rebuild Kits, available where you can get all gaskets, rings, washers in one pack. You can also find gaskets and o-rings for pool backwash valves, in our valve parts department.

Reminder: Always shut off the pump before moving a pool filter backwash valve!

Multiport valve leaking

Waste Line Leaks: In some cases, a bit of debris can become lodged between the diverter and the spider gasket, and cause a small leak to continue out of the waste line. Shut off the pump, and push down on the handle, which will usually flush out the gasket. If the leak continues, you most likely have "blown a gasket". Remove the lid and handle assembly from the valve body, by removing the 6 or 8 screws on the cover, and inspect for a warped or damaged spider gasket. New spider gaskets are installed flat side down, and glued in place with dabs of super glue or silicone. Do Not install a valve on the backwash line to stop such a leak, because a bad spider gasket will cause filtration problems, allowing water to bypass the filter, and secondly, someone will forget to open the valve when backwashing, and cause other problems.

Cover Leaks: Beneath the multiport lid or cover, there are several washers, a spring to give tension to the handle, and some stem o-rings on the stem that connects to the handle. One or more of these may need to be replaced. You can also purchase a Key Assembly, which is every-thing that comes out of the valve body when you remove the cover screws and lift it out by the handle. You can view all available parts for your filter backwash valve in our valve parts department.

multiport valve positions

  1. FILTER: Keep it here 99% of the time, except when backwashing, rinsing or wasting.
  2. RINSE: Use this setting for about 20 seconds after backwashing to rinse tank.
  3. RECIRCULATE: Use this if the filter is broken; at least you're circulating the water.
  4. BACKWASH: Use this setting to reverse the flow in the filter and send water out of the waste line. Make sure valves are open or hoses rolled out.
  5. CLOSED: Put here to close off flow from the pool, usually to work on the equipment. Do not operate pump with valve in closed position.
  6. WASTE/DRAIN: Another filter bypass setting (like Recirculate), but this setting sends the water out of the waste port, instead of returning it to the pool. Used to lower pool water level or to vacuum to waste for fine, silty debris or algae.


When it comes time to replace old pool filter valves, be sure to buy the correct replacement valve. Multiport and Slide Valves are not interchangeable among brands, and DE filters and Sand Filter valves operate in reverse order and cannot be swapped. If you cannot identify the correct valve by a label number or other stamped part numbers, you can work backwards from the filter make/model and select among valves that fit your particular sand or DE pool filter.

You can convert or switch from a multiport valve to a push-pull valve, or vice versa, with some light plumbing to reconnect pipes from the pump, return and waste lines, but be sure that the valve is made to fit your filter. The bulkhead spacing and thread size differs by make/model, and valves are often available in both 1.5” and 2” ports, threaded or slip socket.

For very old filters with obsolete filter valves, you can either replace the entire filter, or you can find a push-pull valve with similar bulkhead spacing and pipe size (1.5”or 2”), and hard plumb it, or use sturdy rubber couplings to connect to the tank bulkheads (pipes or fittings running in/out of filter tank). You can also hard pipe the SP710XALL multiport valve to any side mounted sand or DE filter. For top mounted valves used on sand filters, there is no proper way to retrofit a replacement valve, and filter replacement is the only option for obsolete top mounted valves.

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