Jim,
That is a general question to anyone using a pump filter system. I've never had to use a secondary filter or purify any further. I only filter mountain stream water, above 9,000 ft, & have never been sick either. When above 12,000 ft I don't filter @ all in clean moving streams or water coming directly out of rocks.

If you're trying to kill/remove viruses, you'll have to use a purifying system like the SteriPen, First Need, chlorine dioxide tablets, Polar Pure, etc.

Jeff is that a question to me or others?
(Do the people that use a pump filter system further treat their water with a "SteriPen" or tablets?)

I would tend to trust the water after filtering rather than not especially in some of the mountain streams I would use (I have also never been sick from water) however a video I watched does say that it does not filter virus so just curious how concerned I should be with further treatment.

I've been using this system all summer with very positive results. I trust it just as much as a pump filter. Look @ it this way, gravity is gently moving the water through the filter rather than me forcing it through with a pump.

Do the people that use a pump filter system further treat their water with a "SteriPen" or tablets?

The filter element is good for a subjective 1500 liters.

I've already posted them!

The tube is actually 12" long not 18.

Rather than destroy the original clean side water tube by cutting it in half, I called Cascade Designs & they sent me a whole new tube which I cut to 12" & attached the black plastic shut off, which they also included. I then attached this new tube assembly to the clean side, white nipple connector, on the filter. This eliminates the clean water bag & saves about three ounces.

I'll post a photo.

This is the configuration I use. It works great plus it's lighter. I will post a picture! Promise.

yes you can attach a smaller bag, but then you have to switch from the drinking hose to to filter hose then back to the drinking hose everytime you collect water. according to jeff down below you can attach a drinking hose directly to the filter eliminating the need for the second bag all together

I have already used it and think it is a great system. It will filter just under 2 liters a min. Cleaning is a piece of cake. All you do is filter some water then take the clean bag and move it higher then the dirty bag. After this process is done just dump out the dirty bag and your filter is clean. The important thing is not to leave water in the filtration cartridge if you are going to have a freeze at night. This will damage filter. I hope this helps just let me know if you have any other questions.