The red bit is a double ended screw – it doubles as both a bung/block for the hose to prevent oil loss, but also allows you to attach another hose to it to feed it through. The principle being that you :
Remove the remote.
Attach the red double screw bit
Thread another hose (old hydro hose) through the frame etc. until it pops out the seat tube at the top.
Attach the reverb hose to that old hose using the red bit, and then pull the reverb hose back through the frame (as its now attached to the old hose)….
EDIT but you knew all that anyway having watched the video 🙁
If you want a connector drop me a mail (Ben@birdmtb.co.uk). I have loads.