I don't have any photos, but a flopjack is simply a bucket suspended, perhaps between the passage walls, that fills slowly from whatever water source available. You suspend it so it will tip when it gets near to full, roughly halfway down the bucket. Once you get enough water in it rather than overflowing the whole lot is dumped, either directly onto the dig face or into a pipe via a collector which you can reposition as needed.
You may need a bit of trial and error (easier on the surface) to get the right mounting points and method of suspension.