Thanks for a great wee video clip. IMHO, one of the simplest and most elegant demonstrations of curved earth out there. It seems more intuitive than the Bedford Level experiment, and far easier to set up in your back-yard.
To avoid arguments with surface refraction being used as a confounding variable, this system appears to be portable enough to set up on a hill/mountain top. Even literally with DIY materials: 15 feet of clear plastic tubing, two stakes (and a heavy lump-hammer), some cable ties, and 10 litres of water give or take.. Given there seems to be some disagreement/wilful confusion from FE folk about what constitutes 'eye-level', this arrangement should create an agreed 'level' to use. (The point at which someone won't commit to even this basis, is the point you should probably leave them to their own little world...).
Combine that with the view of the horizon, and high peaks in the vicinity (great example thread here I found earlier today)
https://www.metabunk.org/threads/using-mountain-ranges-to-predict-the-shape-of-the-earth.8800/ (a wee nod to the work Rory put in calculating all those numbers)
and I think anyone has an easily presented, hard to refute case for globe earth...