i store them anyway they get laid down.  And I have a lanyard where it sits upright about 99% of the time and haven't had any leaks.  I will also pop the battery off to charge at night and just set the atty/tank standing up on the desk, and have never had a drip when I picked it up in the morning.  
I also don't use a syringe to fill, just pop of the tank end, and now close to 3 months with the same tanks, no problems.  
Brew