Like everyone else has mentioned, any 10ml bottle works fine, I too got some from fasttech. I actually like these better than the stock ones, they were too soft, especially after a couple of uses, you literally have to hold down on the bottle for days to get liquid up in your atty. On one hand it's nice because you can a .... load of extra bottles on hand for dirt cheap, unfortunately you do have to reuse the top cap of the stock bottles. I've searched everywhere for some sort of reasonable replacement, it's just your average top with an extended tube, its such a simple piece I thought there would be something out there, but no luck so far. I feel like if you got the right size tube there would be some way to connect it so it would work. I just got my third Wraith yesterday, which gives me 6 caps altogether, so I fell like I'll be alright.