So I have a first needs XL purifier (http://www.rei.com/product/767831). Except for the weight I really like this thing. It takes everything out of the water but the water. I keep poking my head around looking for something much lighter (I dont want to do the chemical thing) but am never overly happy with what I see. It seems like most systems a just a little lighter with a large sacrifice on filtering capabilities. I've been curious to try the Sawyer 3-way inline filter (http://www.rei.com/product/801824). I would turn my hydration bladder into a "dirty water" holder and attach the sawyer to the hose and suck out clean water. I was at rei today looking at this when all of a sudden I began to wonder why I couldn't do this same thing with the first needs xl replacement canister (http://www.rei.com/product/767833). This would be a very large weight reduction and keep me from buying another filter. I know this is bigger and more bulky than the sawyer but I'm curious to try it. I'm posting here because surely I'm not the first person to think of or tried this. Any comments?

HEAVY!

Cheers

Even just the filter is heavy - 8 ounces?

Sawyer is 2 ounces?

You also have to include the weight of the extra bottle and hoses. You need a large elevation change, like maybe 6 feet?, to get the water to flow at a decent rate.

In the U.S. you only have to worry about Giardia, maybe bacteria, the smaller filter pore size for viruses is not needed.

I recently got steripen adventure opti which seems to work okay, weighs 3.6 ounces

I played around with this at one time, thinking along the same lines as you. The First Need is a great purifier; I have one from years past that I used exclusively for a long time and in numerous countires.

The good news is the first need purifier cartridge fits the standard hose diameter used in drinking tubes...

But, the First Need needs some pretty good water pressure to push the water through the filter cartridge at a reasonable rate and gravity alone doesn't seem to cut it. I found that I could only get a faint trickle through... something on the order of 10 min/liter... or worse.

I've heard there's a similar problem with the Sawyer purifier (not filter) unless you prime it at first at home via the kitchen sink and keep it wet throughout your hike.

Ultimately I settled on a gravity filter set-up using the sawyer filter which works well (the slightly larger filter screen/pore size makes all the difference in speed) albeit, it doesn't remove everything a purifier would.

Just recently I've switched to the Steripen Adventurer Opti, which I'm very happy with so far.