Advice on Derwent Macadee 3 part flush unit functionality?

The Derwent Macadee flush unit is working but I want to increase the amount of water released when flushing but cannot see how to do this.
The unit has the usual functionality but has as an appendage which comprises a vertical tube with a hole in it, and a piece which is pulled up by the flush lever and then falls as it has a weight. The top of this appendage has a rubber tube running from it to the top of the main water outlet tower. (Please Excuse any incorrect or confusing terminology .)
I cannot find anything like this appendage online., and it’s presence doesn’t seem to make any difference to the unit functionality. I have disconnected it.
Advice very welcome.