The same works for the first need water purifiers. I have one of the extreme gear camelbaks (military version) and the drinking tubes all come with a quick disconect at the bite valve so they can be plugged into a gas mask. Anyway I picked up a second quick disconnect piece and attached it to the 'out' plug on the filter, now I don't even have to worry about spilling the water thats still in the bag, I just turn the valve off, disconect the mouthpiece, plug in the filter, turn the valve on and pump. Great idea cactuscat.
By the way, I have used the camelbak mule, blowfish, and hawg, and I have found the military line of bags to be far superior in ruggedness, duribility, and functionality to the other models. Of course the price tag reflects this, but I would say it is worth it. These models are not readily available at stores but they may be special ordered through Larada's Military Surplus. I use the Transformer model, It has three detachable bags that can be used in any combination for a range of capacities (110ci, 500ci or 950ci). The bladder holds 102oz (3.1 liters). This range is enough for the same bakpack to be used for short hikes, overnight summer trips and everything in between. More information on both military and civilian models can be found at http://www.camelbak.com