If you cut the screw top off the Platypus bag, they will fold flat and much tighter. Not Altoid tight, but definitely mess tin tight.

Crush the micropur tablet while it's in the packaging. Take your razor blade and cut it into thirds, each third for one 10 oz. gerber bag. Put the remaining crushed tablet back in the small packaging and seal it with a small piece of duct tape. That is what I would do.

platypus are great light weight and compact containers, but not as durable as my naglene. I have managed to crack the plastic of the tube attachment from the hydration version, delaminted the plastic of the some and even put so much wear one of the folds from one of the bottle, that it started to leak. The platypatches could not repair the hole. I'm still using platypus containers, though....

I wander if if would be possible to have some sort of strips of plastic looped down from the opening so that you could prefilter the water with a coffee or other simple filter...
The strips would make this a lot easier and prefiltering the water goes a LONG way into making any of the chemical treatment completely effective.