What? You got a Protank to not leak!? How?
We went through counseling. Through trial and error. This is what works for me with a ProTank 1 (I don't know about the other versions).
When I turn it upside down to fill it, I slide a Q-Tip up inside the tube to block any juice. I fill it up to just below the bottom metal band. After I put the cap back on and flip it over, before I put it on the battery, I lightly draw though the drip tip. If I hear a gurgle, I gently blow out the excess into a paper towel. I keep doing that until I don't hear a gurgle. After putting it on the battery, I take another cold draw and listen for a gurgle. If I hear one, I take it off again and blow out the excess.
While vaping, I never let it get more than 2/3 empty and pay attention to if it gurgles (if it does, I take it off and blow it out as before). I also make sure the Protank is room temperature when I use it. I don't know why this works for me, but it does.