I just got back from a 5 day 3 person backpacking trip in Lassen National Park. We used a Sawyer Squeeze for all our water. I had 2 Evernew 1.5L water bags and the largest Sawyer bag for the dirty water bag. My friends had various other containers for clean water. I also had the Sawyer adapter from Mini Bull Designs (Tinny). None of us got sick drinking water filtered by the Squeeze filter, and I could see what appeared to be little crustaceans and other minute critters swimming around in some of the water.
I may have been a little overzealous with my squeeze pressure because one Evernew bag sprung a leak where the neck is glued on, although the bag is 3 years old, which is 90 years old in human years. When using the adapter from Minibull, I noticed the Evernew bag seemed to blow up like a balloon indicating excessive pressure, which probably contributed to the leak. After that, I backed off on the adapter one turn to let the excess pressure go through the threads. That solved the problem and the other Evernew bag didn't leak. Strangely enough, the much maligned Sawyer dirty water bag didn't leak at all.
The Mini Bull Squeeze adaptor works great for back flushing in the field and I plan to continue using it, although I will back off one turn in squeeze mode where the clean water bag fits on as I said before. Also a cut down plastic soda bottle is essential for filling the plastic dirty water bag in the field because you will go bonkers trying to fill it without one. If you blow it up with your mouth first, and who wants to put his lips on a dirty water bag anyway, it just collapses when you submerge it in the water.
I can tell you one thing, squeezing enough water for three people through the Squeeze filter every night and morning is tedious, unless you have forearms like Popeye, which I don't. I noticed that water flows through it at a reduced rate with no squeezing at all, so I think rigging the Sawyer filter as a gravity filter is a good idea, as gravity should push the water through the filter eventually. It would sure make life a little easier.