For sale, Outward Hound Hydration Pack. This is a camel-pack style backpack for your dog. It looks like a regular pack (and could be used as such) but it has a removable bladder that you fill with water. There is a tube that is attached to the bladder for you and/or your dog to drink from. There is also an additional pocket for whatever you need to carry - treats, poop bags, spare leash, etc. This pack very comfortably fits my 50lb dog and is fully adjustable. It has actually never been used. I'm asking $10.
Shipping is $7.
The bladder part: