I was slightly annoyed that seek outside doesn't make hydration pockets (except in gila) so I had to make one myself. I filled my Source WLPS three liter hydration bag and measured the neccessary amount of cloth by wrapping cloth around it
I made a pocket where to insert an aluminium tube which mates the hydration pocket to the backpack. All this is non-destructive.What I had to do for the tube, I sewed (by hand) a 5x7cm velcro patch to the side of backpack, punched two holes 3cm apart with a belt hole iron, and cut the cloth open between them. Then I sewed around the hole with buttonhole stitch. A velcro protects the hole and tube entry. I made probably more than a hundred new holes for water to get in so the backpack is no longer waterproof though
[img]https://hakkarainen.kuvat.fi/erä/unaweep_hydration.jpg[/img]
Some kind of double cloth solution might have been better, but velcro was what I had in hand.
If the img tags don't work maybe url works? [url]https://hakkarainen.kuvat.fi/erä/unaweep_hydration.jpg[/url]
If that doesn't work either just copy/paste for some images.. https://hakkarainen.kuvat.fi/erä/unaweep_hydration.jpg