Quote Originally Posted by TheMudMan
18 gauge tear the rubber up on the vials........ you will end up with nice big holes where some of the rubber will be in the vial or the oil will seep out of the top of the vial.

20g works fine........ doesn't tear up the rubber and it's big enough to draw up the oil without any problems.
Not saying this isnt true, but I have never encountered this problem, as long as you keep them right side up there shouldnt be an issue, either way 18 or 20 will work just fine.