Doesn't a flush require that water be added fast enough to eliminate all the air from the bend? Otherwise, water will just trickle out at the same rate it trickles in.
Why did Britain evolve such a complex mechanism when this pattern seems so simple? Water economy: these valves can leak and can be kept permanently open, allowing precious gallons to be wasted.
I've never been to Britain, but my impression is that it's not a particularly dry place. Why would "water economy" be so much more important there than in e.g. Israel or California? Perhaps toilet technology is as path-dependent as any other evolutionary process?
