Hard water bottle for gravity filtering?

I'm not sure if this would work… (but it does have a one way valve in the cap to prevent vacuum). The Blue Desert SmarTube Bottle Hydration System.

They are available on Amazon for about $10.
http://www.amazon.com/Blue-Desert-SmarTube-Hydration-System/dp/B000GM6LWS/ref=sr_1_1?ie=UTF8&qid=1405081908&sr=8-1&keywords=smartube+hydration

Stephen Barber did a write up on them here:
http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=91087

I picked one up and I really like it. I've never been a fan of the whole bladder in my bag thing.

Good luck. Let us know what you come up with.

This may not be exactly what you're asking about, but I made a gravity filter out of a dry bag and sawyer mini.

There's pictures here:

https://plus.google.com/photos/103791727089052489446/albums/6034994606405476289?authkey=CPLs366kt4LLZw

You can hang the bag up and use it as a faucet.

I've used this set up on a couple trips and it's worked flawlessly. 5.5 oz with the sealline storm sack. You could probably get a lighter or smaller bag, but I'm using it for a few people usually so I went for a gallon bag.

C.

Here’s what I came up with. Prototype works good, but I’ve never actually tried it on the trail.
Check valve