A couple of insights:
1. This filter has charcoal in it which means treating first, filtering second is the right way to go. Treating kills the "small stuff" or viruses, then filtering removes the "big stuff" and the charcoal removes the chemicals that have already done their job so you don't have to drink them.
2. Since the charcoal removes the chemicals, there's no point in using expensive tablets. Unscented chlorine bleach will kill viruses in about half an hour. 3 drops per liter of clear water, 5 drops per liter of cloudy water. Once it's done it's job, you run the water through the filter and the charcoal removes the bleach and you get purified, fresh tasting water.