I noticed the same thing right away, it seemed to leak a bit around the top cap. Not sure what did it but that went away after I screwed it on and off a few times. Due to the design of this tank I figured right from the get go that I should do my best to keep it upright and I haven't had any problems with it. I actually purchased it at a brick and mortar with intentions of bringing it out that night (a week ago today) to show it off at my gig. In the end, I stared at the thing for a day and a half before I decided to fill it up and go for it.
I am using the Drunker Tank on my Vision Spinner 1300mah, with an ego lanyard. I tend to keep the lanyard around my neck most of the time and the weight of the spinner allows it to hang at an angle which does not seem to be too much for it and create a leaking situation. When in doubt... if wearing a shirt or jacket with a breast pocket that does the trick for me as well. The other night my Spinner needed a charge so I swapped over to my Smoov XL 650mah battery (which I need to discontinue use of asap). This becomes a very top heavy setup. With the lanyard in use I leaned over to dig for a minute for a decent pair of socks out of a bin of clean laundry, didn't think about the device hanging upside down until I was finished and saw a noticeable drop in liquid level and nearly a mouthful (oops) of juice. So.... Keep the thing upright if you can. As the liquid level gets lower... I'm almost empty right now... I find myself rolling it as I would with a stardust or other similar top coil clearomizer to coax more liquid to the coil. I'm not sure as I have only used thicker liquids in my Drunker Tank to this point if this is necessary if using a liquid thats on the thinner side. The wicks seem to work really well under most circumstances.
Besides the issues you might experience with leaking on this tank, at 4.8v on my Spinner this thing has great vapor production and the cleanest flavor I have had yet. I find any potential issue with leaking to be negligible due to the wonderful experience I am having while using this device.