For me, the leaking is intermittent and seemingly without reason. But....
After you fill the tank, wipe the outside completely dry with some tissue or a napkin, including the little filler hole. Any liquid on the outside of the tank may end up in your mouth or on the battery. This seems to work almost all the time for me. I can go days without a leak.
I haven't tried the comment above about keeping the fill side of the tank higher and pushing the battery down on the tank.
This sounds like a great idea though. It has the same effect.... no liquid leaking to the outside of the tank.
Also, try filling the tank only 1/2 to 2/3 full.
Also, try a new tank.
Despite this one problem, I think the tank system is vastly superior to anything else I've used, especially the ease of draw(!) and lack of filler taste .( I have a type A tank from Liberty Flights on a 650 maH eGo, but going to try a Type B when one of my two atomizers burns out, as some say they're better.)