The 4 vids I've watched so far are all the same 'review type' tutorials. I will note that in the review I watched shortly after unboxing the tank, and the ones that I've just watched, I agree with the reviewers that the tank is beautifully crafted.
The two different types of 'filler bottles' I use are a 30 ml one and a 10 ml one. Both are 'needle tipped', with the tip of the 10 ml bottle being smaller (in diameter) than the 30 ml one. The tip of the 10 ml bottle fits all the way into the filler hole, with some 'headroom' to spare. The tip on the 30 ml bottle won't go all the way in like the other, but it does go down into the filler holes cone a bit.
With my first fill I used the 30 ml bottle and the top cap was on (so there was only a little or no 'air escape point'), but like I said before, during the refill it didn't matter whether the cap was on or off or which bottle I used. The only way I could refill it was by pulling one of the wire ropes out and using its' hole, so airflow may be the issue here. The tip on the 30 ml bottle completely covers the fill hole, and the first fill went fine.
I already checked the whole 'fill passage' and it looked clear, but I'll do it again at some point in the near future.
Thanks for the 'page request' Katya, the suggestions Daniel, and since a refill executed fine by using one of the rope holes (which is a lot bigger than the fill hole) maybe (but actually probably not) a drill will come to be used Nailz.