Well, I fitted it all in this weekend, and after a couple of false starts with the bloody thing leaking via the bolt holes for the cistern to pan coupling bolts, it all seems to (basically - more in a moment) work. The water does indeed flood into the cistern predominantly from the bottom of the tower - and very quickly, too. Now, this dangly thin pipe that comes out from just under the top of the tower. I left it just hanging where it wanted to naturally, and shortly after the fill cycle began, water started to pour out of this pipe 'in parallel' with the main water coming into the tank from the bottom. I left it to continue filling, and the water level came up over the end of the pipe. Nothing seemed to happen - it just carried on filling. When the water reached the float level, the inlet shut. I then flushed, and that was normal, as you would expect, as the flush unit is completely separate from the fill tower. As it refilled, I this time held the tube above the water level. As before, water poured out of the tube. When the float level was reached, again the inlet shut, and water stopped pouring from the tube. So, in summary, I still don't know what this tube is for, or where it should be positioned. It doesn't seem to affect the operation of the inlet valve whether it is left above or below the water level. It would, of course, have been handy if there had been some instructions with it ...
Can't remember if I mentioned before, but I had a look in the cistern of my B&Q Bog-to-Go in one of the other bathrooms, and that has a stub tube in a similar position, but no dangly bit of tube attached, so always above water level.
While we're still inside the bog cistern, it seems to me that the dual flush system doesn't work as I was expecting. If you press the full-flush half of the button, that's what you get. A full flush, even if you just stab the button long enough to get the flush established. However, if you press the short flush button, the flush starts, as before, but as soon as you let go of the button, it stops. If you hold the button, the cistern will fully empty. The auxillary adjustable float on the side of the centre section of the flush unit, is set to about half way, and is well below the full water level, so is trying to float, which is pulling up the long rod attached to it. The float drops as the water level passes it, if you keep the button pressed.
What am I missing here ? Why does the flush not 'establish' when the short-flush button is pressed ? Again, some instructions would have been handy ...
Arfa