Well with the carts I have they have 2 hollow vents on them, and if you file as you are saying it weakens the plastic too much and is why I only drilled a simple 1/4" hole rather than a full 5/16" which fits perfect inside because it weakens it down. So I would suggest 1/4" or not filing out the entire cart to have one that lasts.
Another thing you can use if you don't have a drill and you want to test a drip tip style is use a pen grip (with or without the pen tip) I do believe it orginated as the DDC by name, but the way I use the grip, is alone, it vapes better and you're not blowing thru the pen tip to get the liquid to the atty.
I see pics on this, but haven't seen a full video, so I'll compile one on the Grip Tip style drip tip as well.
I know it's rough to tell, but I'm a girl

sorry to confuse you. LOL