I built a wood saddle that I can clamp together and adjust the drill depth to just barely pierce the tube. I then drilled a 1/16 hole level with the top of the bridge. Didn't want to punch a hole as that would leave a dimple that would hinder my flow adjusting method.
I use this 5ml tank D & b gold has echo-e cartomizers! with thick end plugs and a fill hole hence I'm able to move the tank up and down on the barrel to cover the hole or any portion of it and can fill it without disassembling and the risk of messing up the connection of the tubes. Currently I have the hole covered about 90% and still have to leave the unit laying flat or it seeps, even with all VG. Perhaps the end plug isn't sealing the hole as effectively as it looks.
My next venture with the DC atties will be to drill a smaller hole, experiment by covering part of the hole with a condom if needed in addition to adjusting the tank up and down to cover the hole to try to find a point where it doesn't seep.
If things continue to seep I'll simply fill the tank all the way and only uncover the hole when I need to replenish the atty.