Ok so I'm pretty sure I'm challenged with this. I really don't know if my sponge filter is working or not. If the tube gets completely filled with water then the air bubbles come out of the sponge but otherwise it just bubbles out the top. The video is crap but I hope it explains it. I've never had a sponge filter before so I don't really know what to do https://www.youtube.com/watch?v=_QVm2DfYeB4&feature=youtu.be
The top of the tube (the outlet) needs to be at least 1/2 way submerged. Air bubbles and a small stream of water will be pushed out of the tube. If it's too tall, you could probably just take the "7" shaped part of the tube off..the bubbles might bother your fish though. Does that make sense?