Don’t Ditch Your Sawyer Filter Just Yet
Despite syringe back-flushing regularly, the flow rates of the Squeeze and the Mini dropped much faster than I expected. The Sawyer website states that the Mini has “longevity up to 100,000 gallons.” Mine lost most of its flow long before it had filtered 100 gallons. My revelation came on a wet and windy day in southern California, while sheltering behind a tree next to Deep Creek. As I cursed my flagging filter and frozen fingers, I realized I’d assumed “longevity of at least 100,000 gallons.”
After returning from the PCT, I emailed Sawyer customer service, asking for details about their warranty. They side-stepped the question, but the reply did contain a link to a video about back-flushing. The useful section starts around the 1:40 mark – treating the filter with hot water and/or vinegar. The methods shown in the video need a little fine-tuning, so I modified them slightly. I also looked online to see what else people had done to restore their filters.
Hot Water (HW) Treatment
I won’t go into too much detail, because this treatment was extremely time-consuming. It certainly wouldn’t be practical during a thru-hike. Although it was pretty effective, it didn’t get the filter anywhere close to its original flow rate. Basically, I spent ten hours microwaving a bowl of 140℉ water with a Sawyer Mini floating in it. I back-flushed the filter with hot water every 20 minutes and cooled it down to measure its flow every two hours. After six hours, the filter had improved as much as it was going to.
Vinegar (VG) Treatment
Vinegar is typically only 5% acetic acid, and I didn’t want it further diluted by water already inside the filter. After back-flushing, I forward-flushed the remaining water from the filter using a CNOC Vecto full of air. I then screwed the filter onto the plastic vinegar bottle, turned it upside down, and squeezed some vinegar through the filter. After a half-hour, I squeezed some more vinegar out and left the bottle upside down for another half hour.
Knock-on-Wood (KW) Treatment
I forget which website this suggestion came from, but I’m sure it’s not Sawyer-approved. However, this method was quicker and more effective than the hot water treatment. First, I made a stopper for the inlet side of the filter. I used:
- the end of a pen
- a small length of tubing
- the inline coupling from a Sawyer Squeeze
I back-flushed the filter, capped the outlet, inserted the stopper, and repeatedly knocked the filter against a block of wood. I hammered away for about 30 seconds, or until my forearm got tired. Then I back-flushed the filter into a white bowl. I repeated the procedure until the back-flush stopped producing debris, almost an hour later. Obviously, there’s a risk of damaging the filter if you hit it too hard or strike it against a surface that’s too hard. I was careful to make contact only with the black plastic collar at either end of the filter.
Below, the table on the left shows the history of the Sawyer filters I used going SOBO in 2021. The table on the right shows how long each filter took (min:sec) to fill a 24 oz. (0.71 liter) bottle. The corresponding flow rates are also shown. I squeezed water through the filter using a CNOC Vecto, timed it using a stopwatch, and rounded to the nearest five seconds.
- Rows 1&2 – after 800 miles of use in southern California, the Sawyer Mini retained only 22% of its original flow.
- Rows 2&3 – the Mini didn’t benefit significantly from vinegar treatment. The Squeeze experienced a 2.5x flow improvement.
- Rows 3&4 – hot water treatment restored 47% of the Mini’s original flow.
- Rows 4&5 – knock-on-wood treatment restored 90% of the Mini’s original flow.
After gathering the data, I filled the 24 oz. bottle five times using the Mini to check repeatability. Here are the timings: 53, 54, 48, 52, 51 seconds.
I spent 43 days on the PCT in southern California, filtering less than two gallons per day, and back-flushing once per day on average. In other words, the flow rate of the Sawyer Mini dropped to 22% of its original value after filtering less than 86 gallons. Treating the Mini with hot water was partially effective, but very time-consuming. It’s likely I could have restored the Mini directly to its final 90% value using only knock-on-wood treatment. In the future, I’m going to knock on wood every time I back-flush the filter on trail. That should prevent it from becoming too slow.
I live in a hard-water area, and when I allowed my Sawyer Squeeze to dry after the 2020 season, it’s likely that mineral deposits formed inside. In the future, after storage, I’ll dissolve those minerals using vinegar. (Alternatively, I could back-flush the filter with distilled water before letting it dry prior to storage.) The Sawyer Mini didn’t benefit from vinegar treatment because it didn’t contain hard-water deposits.
I didn’t know it at the time, but the Squeeze was slower than it should have been after vinegar treatment. It had only filtered about 10 gallons more than the Sawyer Mini I treated later. Despite the Mini’s smaller diameter and similar length, it was faster than the Squeeze. The two most likely explanations are:
- The Squeeze was still suffering from some sort of storage-related blockage. (“Lifetime Warranty” or not, I’d thrown the Squeeze away after completing WA+OR, so I couldn’t investigate this possibility.)
- Back-flushing the Squeeze is inherently less efficient than back-flushing the Mini.
Back-flush: Squeeze vs Mini
To properly compare long-term filter performance, I should have measured their flow-rates side-by-side. However, I’m not going to let that stand in the way of some educated guesswork.
- I never thought to measure the Squeeze’s initial flow rate, but I can estimate it. I’ve used the flow for a brand new Sawyer Mini, increased according to the dimensions from Sawyer’s website. Mini Diameter = 1.35,” Squeeze Diameter = 1.9.”
- I’ve assumed the flow rate of a Sawyer Squeeze that’s filtered 86 gallons is the same as a Mini. I’m giving the Squeeze the benefit of the doubt and ignoring any potential storage-related blockage.
- My Sawyer Mini was back-flushed approximately 43 times, and I’ve used the same value for the Sawyer Squeeze.
- Back-flush efficiency might improve slightly as the flow-rate drops, but for the sake of simplicity, I’ve assumed it’s a fixed value for each filter. I’ve only found one reference to back-flush efficiency, and it happens at the 1:10 mark in the video. “A good backwash can restore up to 98.5% of the filter’s flow rate.” (Well, fool me at least twice, shame on me.)
It’s likely that back-flushing the Sawyer Squeeze is less efficient than back-flushing the Sawyer Mini. As a result, the Squeeze and Mini flow-rates quickly converge. Knocking the sh*t out of a Sawyer Squeeze when performing a back-flush is probably even more important than it is for a Sawyer Mini.
This website contains affiliate links, which means The Trek may receive a percentage of any product or service you purchase using the links in the articles or advertisements. The buyer pays the same price as they would otherwise, and your purchase helps to support The Trek's ongoing goal to serve you quality backpacking advice and information. Thanks for your support!
To learn more, please visit the About This Site page.