I have a box full of those same beads/crystals on shelf in my garage. Tested them for finish drying Biodiesel some years ago. They do a great job absorbing water out of a fuel as stated. The material swells up to like 10x size of the dry crystals. Is also the same material used in some potting soils to hold moisture.I'll try and dig up the actual name and manufacture info I tested.

That said, I stopped using them for commercial fuel drying because we noticed shards or what ya might call a "dust" off them passing our 10micron filters and showing up in finished product filters. The crystals are not uniform when dry, so some of those passed through the socks and screens we were using to hold them. If that issue has been resolved by sifting and screen sizing from the manufacture above, then I see no reason they wouldn't work as stated in a fuel tanks for winter storage.I was pumping thousands of gallons of fuel through them, rather than just dropping in a tank.

Just my 2c...

Here is those beads I tested. These ones are stained from BD filtering, and a bit moist cause the container wasn't sealed air tight. But they are infinity reusable if you dry them out. If anyone want's to play with them, I'll mail ya a baggie full.

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If I remember right, inside the screened container was what appeared to be a rod...not granules or beads. Does this rod expand with water to fit the container?

That's a design I haven't seen before. But would guess it's a similar material. These beads swell up like jelly beans when you soak them in water.