Hanna all I can say is I don't know what kind of e-cig that man in the video or you have. I had a mini it was an m402 you had to push the inner cart out with a paper clip and than you could take the filler out put a few drops in put the filler back in and I always pushed it down in the juice than pulled it up so it would touch the atty when put back together.
If you have no flavor that's strange I guess I never looked for a non flavored cart, but I've looked in to no flavor juice for mixing.
I wish I could help more, I suggest you look at the review section on this forum and see if you can find your brand, and if not there are plenty of videos that show how to fill and top off different e-cigs something has to be close to what you have.
I watched the video again and that is a different cart than any I have seen it looks like a holder for the filler that he pops out so he is not touching the liquid when he does that. Do you have the same e-cig as he does? do you have eliquid? if you do I would deffently pop the cart out and place a few drops in it and see what it does, I would hate to think your vaping on nothing it would not produce vapor and vaping with no flavor can't be very good when there is a lot of great tasting juice out there to use.
Hope you get this figured out and I'll check back on this thread later to see how your doing.
-Dan