Butput an inline filter between a hydration bladder and yourself? I'm not convinced anything like that will work, even if you could put such a system together. The reason: You need to have some kind of pumping action to push the water through the filter. In the SafeWater system or Exstream bottle, that comes from a combination of sucking on the bottle and squeezing it. Trying to pull water through a hose AND a filter with suction alone isn't going to be possible. You'll be hiking or biking around with your cheeks caved in.
What to do? Pump filters are the obvious solution, but you must have your reasons for not wanting to go down that road (weight, perhaps). That leaves you with chemical purifiers, such as Potable Aqua ($8 for 50 tablets plus taste neutralizer; www.rei.com). That stuff kills just about anything.
More water-filtering advice and product reviews can be found in Outside's 2004 Buyer's Guide
Filed To: Filters and Purifiers