once in a while those little tanks will leak when you take it off as the seal does not seat itself. you can either hear it leaking or do like i do and spit on it and see of you see any bubbles. if its leaking just reconnect it and disconnect it until the seat sets itself properly, once sealed it should not leak at all.
X2I refill my tanks and this cause's the seal in the tank to leak sometimes. I got some "Mac Caps". solid brass threaded cap with a seal. Even if they try to leak nothing comes out.
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