I have a Sawyer mini that I have had for probably 6 years. My last trip, the flow was reduced to a drip. It still filtered, buy took maybe a 1/2 hour for a liter. I tried back flushing and forward flushing with no improvement. On the forward flush, the water would barely shoot out. I started with a diluted vinegar solution soak with little success. Then I backfilled the filter with strait vinegar and left it soak for two hours. Then I back flushed it once and then tapped it fairly hard on my deck step as I rotated the filter as recommend on one video to dislodge sediment. To my surprised, on the next backflush, some tannin stained water came out. I tapped and back flushed six more times, then forward flushed. This time the forward flush shot out about 4 feet. I then tested the flow and it was much better. This filter was headed for the trash bin, but it's now going on the next trip.

I have had many of these filters over the years. This is what I do for filter maintenance. I find that if you back flush after every 5 gallons or so the sediments do not pack the filter so much with debris . At the end of every trip I back flush it with fresh water at home with a few drops of regular bleach in it. This is so the tannins don’t dry up in the filter, and the bleach sanitizes the filter so nasties don’t grow. Glad you got your filter working again.

This is good information folks. Thanks for giving me a few things to try.

I use a 15:1 water to bleach solution. That is what I have used to clean up blood spills at work back in the day when I was still a clinic nurse. Then rinse by running clean water through and let dry.

Impact to filters will damage its hollow fibers. Flow will increase because the dirty water is now bypassing any filtration. Check out possible damage by performing the integrity test here (beginning at 0:54):
Care and Maintenance of your Platypus GravityWorks™ Water Filter
Yes, this is for a Platypus filter, but any hollow fiber filter requires similar TLC to prevent fiber damage. I can't believe intentional banging on hard surfaces to be recommended. Video link?

schweady: "Impact to filters will damage its hollow fibers. Flow will increase because the dirty water is now bypassing any filtration. Check out possible damage by performing the integrity test here (beginning at 0:54):
Care and Maintenance of your Platypus GravityWorks™ Water Filter
Yes, this is for a Platypus filter, but any hollow fiber filter requires similar TLC to prevent fiber damage. I can't believe intentional banging on hard surfaces to be recommended. Video link?
"

It's a bit more complicated than that because you seem to be assuming that all hollow fiber filters are equivalent. That isn't true. Sawyer filters are designed to have a longer use life and are more resilient than most other filters. Gentle impact is part of the suggested back flush process and it does not notably reduce use life.

Sawyer filters are not primarily produced for recreational backcountry usage. They are produced to provide safe drinking water in areas that do not have water safety infrastructure, including large cities. The amount of usage that a BWCA paddler gets from a Sawyer absolutely pales in comparison to the average Sawyer filter user. Gentle tapping is a necessary part of the long term maintenance and helps to provide safe drinking water for years.

For example, I recommend that you watch this video. At the least, jump to ~26 minutes for a section on training users on how to back flush the filters. These people would not otherwise have clean drinking water. Many Sawyer filters have been providing safe water for a decade or more. They are not being told to break the filters. They are being taught proper maintenance.
Sawyer Squeeze

Edit: OP does mention "fairly hard" banging and that's probably not a good idea in the long run. Tapping against a soft surface, like the hand, while inverted will do the trick.

With my platypus I back flush a litre (of 4) after each use. I also carry a collapsible bucket and let it fit 20 minutes or so to settle and then use it to fill dirty bag. Never slows. Same filter for years.

pleflar: "

schweady: "Impact to filters will damage its hollow fibers. Flow will increase because the dirty water is now bypassing any filtration. Check out possible damage by performing the integrity test here (beginning at 0:54):
Care and Maintenance of your Platypus GravityWorks™ Water Filter
Yes, this is for a Platypus filter, but any hollow fiber filter requires similar TLC to prevent fiber damage. I can't believe intentional banging on hard surfaces to be recommended. Video link?
"

...I recommend that you watch this video....
Sawyer Squeeze ..."

Thanks. Yes, a significant difference between "tapped it fairly hard on my deck step" and "tapping the filter against your palm."