How to Backwash Your Pool Filter—The Easy Way

It’s an age-old rule: what goes in must come out. And with your pool filter, it’s no different. Come on, you have to give it some credit: your filter does a lot of the heavy lifting to get out all those tiny contaminants your chlorine neutralizes. It’s just one of the many parts of your pool’s circulation system that you can thank for sparkling clean water. So the next time you’re floating on your back under a cloudless sky, spare your pool filter a little thought or two.

For all the noble work it does, a pool filter’s sort of like a household vacuum: as it picks up dirt and debris, it holds everything inside, and eventually, it can’t suck anything else in—unless you switch out the bag. And I’m happy to report that in the case of backwashing, you can be fairly hands off when it comes to the actual gunk. I’ll explain what backwashing entails, why you need to backwash, how to know when it’s time, what you need, and of course, a step-by-step explanation to get it done. Let’s get washing.

Sounds Gross! What is Backwashing Your Pool Filter?

Don’t worry—this has nothing to do with sharing drinks, ick! Backwashing your pool filter, also commonly referred to as just “backwashing the pool,” is the act of cleaning out your filter by flushing out all the gunk it’s accumulated. Simply put, when you backwash your pool filter, you reverse the direction of the water flow, and water moves back through the pool filter and out the waste or drain port. Just make sure you’re disposing of it properly—and we’ll get to that soon. All in good time, my friend.

If you’re filter is cleaned out but weak on its circulation, the problem is your pump’s strength. This Blue Torrent 2 HP Variable-Speed Pump allows for a larger horsepower, but never uses more energy than you actually need—it pays itself off in energy saved in under six months and is eligible for energy rebates. Customer Bill Britton says, “Runs great. Super quiet.”

Backwash your pool filter

Why Do I Need to Backwash My Pool Filter? 

First of all, make sure that you have the right pool filter for you. Cartridge users, you’re on the wrong page—though you still have to routinely clean your filter. Backwashing only works filters of sand and diatomaceous earth (from now on, I’ll call this D.E.), which collect contaminants with the help of sharp edges. But once those contaminants build, your filter becomes increasingly less efficient—even if those edges haven’t yet smoothed down—and the pressure of your filter ramps up.

Backwashing cleans out your filter without requiring you to pick through sand, which would be messy, and D.E., which would be dangerous. It also extends the life of your media by keeping your sand and D.E. clean without total replacement—though you’ll need to replace them eventually.

When Do I Need to Backwash Your Pool Filter?

Pool filters usually come with a pressure gauge, and it’s important when you first install yours to take note of it—whatever that number is, that’s your normal operating filter pressure. As time goes on and your pool filter is continuously used, those pounds per square inch (psi) will increase—and that’s a good thing. Think of it like a snowball rolling down a hill: as your filter gets dirty, the contaminants it traps help it trap even more.

But something this convenient can’t last forever—eventually it’ll get so crammed in your filter that it won’t be able to catch much of anything. Generally, you want to backwash your filter once it’s 10 psi over your normal operating pressure.

how to backwash your filter

The Store Again? What Do I Need to Backwash My Pool Filter? 

This one’s easy: all you need to backwash your filter is a backwash hose. Ta da!

Oh, and if you have a D.E. filter, you’ll want a little extra for refilling—but if you have a D.E. filter, you probably have D.E. around, anyway.

Take some pressure off your filter by installing the Blue Torrent MyBot In-Ground Robotic Pool Cleaner: it’s the most economical, high performance pool cleaner on the market—and comes with a lifetime warranty. According to customer David Lain, “Very pleased. My wife loves it.”

How Do I Backwash My Pool Filter with a Multiport Valve? 

Got a multiport valve? This process is super straightforward. Just follow the steps below and enjoy having yet another DIY skill under your belt. And while you’re at it, make sure the filter is never on while you’re turning that multiport valve:

1.     First, turn off the filter system. You don’t want anything running yet.

2.     Then, connect the backwash hose to the filter’s waste port. This will be where the backwash really happens in a second.

3.     Turn the multiport valve to “Backwash.” Yep!

4.     Turn the filter system back on, and let it go for about two minutes. Can you believe it? You’re already backwashing.

5.     Turn the filter system back off, and turn the multiport valve to “Rinse.”  You’re following!

6.     Turn the system back on and let it run for a minute or so.

7.     Again, turn the filter system off.

8.     Restore the multiport valve back to “Filter.”

How Do I Backwash My Pool Filter with a Push-Pull Valve? 

So you’ve got a push-pull valve, huh? It’ll be even simpler for you. Just follow the below steps to get backwashing: 

1.     First, turn off the filter system. Again, it’s better to work when the filter’s off.

2.     Then, connect the backwash hose to the filter’s backwash port. This will be the hub of where the backwash really happens.

3.     Open the backwash gate. You got it!

4.     Turn the filter system back on, and let it go for about three minutes. That’s backwashing. Easy, right?

5.     Turn the filter system back off.

6.     Go ahead and close that push/pull valve.

Part of maintaining a clean pool involves some grunt work, but you don’t have to get hurt in the process. Get all those tight corners with the patented 360-Degree Bristles Blue Torrent Pool Brush, developed by long-term pool professionals. As customer Scott Hinds notes, “Definitely the best pool brush I have ever owned. Far superior to other brushes.”

how to backwash your pool filter

Yuck! Where Do I Put All that Gunk?

Don’t worry if you’re not sure where to put the end of that backwashing hose—this is a major debate. But are you about to toss the product of your backwashing down the storm drain? Let me stop you there. This is not exactly the Wild West, and your local government most likely has an opinion (and some persuasive fines) on where you should put the contaminated water you just backwashed. And chances are: your street and storm drain are a no go. And what about your septic system? Well, it’s totally off limits—unless you want a system failure. That’s a nightmare I’m choosing not to imagine.

Most local authorities are going to recommend that backwash water is collected, contained, and discharged to a sanitary sewer—which is different from a storm drain or septic system—or to a vegetated area contained within your property. If at some point, you switch over to a cartridge filter (you know, the ones you don’t need to backwash), they’ll probably want them rinsed in a sink, bathtub, or over your own lawn or vegetation.

In either case, don’t just take my word for it—all these regulations vary based on where you live. Your local authorities should be able to let you know, and probably have a convenient (if clunky) website with the answers. Don’t you just love government dot coms? 

Want to know how to clean the bottom of your pool? Read more here.

Look, I Have a D.E. Filter. How Do I Refill It?

When you backwash your D.E. filter, you’ll need to replace the powder, which is much more effective to do through the pool’s skimmer. To do this, you want to mix the manufacturer’s recommended amount of D.E. with water to form a wet sludge, and then pour the solution directly into the skimmer. Make sure the pump is running properly so it circulates through your system. It’ll take some time for the mixture to properly disperse across the filter, so you’ll want to wait at least eight hours until you swim again. It’s okay—distance makes the heart grow fonder.

Keep your pool and any add ons in top shape with the 1.5 HP Variable Speed Blue Torrent Thunder Pump. This robust and thorough pump is the most reasonable decision any pool owner can make: comes with a lifetime warranty, is eligible for rebates, and pays itself off in under one year. Plus, variable-speed filters will soon be virtually mandatory by federal law.  

how to backwash your pool filter

Backwash Done. Now It’s Time for a Backstroke

That was all you—and you never had to call in an expert. That procedure was about as easy as they come, especially since you did your research. Now that you’ve learned how to backwash your filter, you have a future of clear water ahead of you. So take a moment under the sun to congratulate yourself for a job well done—just make sure you’ve got on some SPF. Enjoy.


For additional information on how to get rid of mustard algae, check out this article. Having problems getting rid of white water mold in your pool? Read more here.

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