Shires Twinflow Siphon

[3magnet]

Hi all,
My wife and I are doing home renovations and got busy in the bathroom. We lifted the toilet bowl lid, as the loo handle was sticking a bit (due to limescale build-up). We noticed a sticker on the syphon/siphon system saying that: "...this flush system is set-up as a full flush, to change it to a dual-flush system, remove the plug above the syphon/siphon bowl."

The syphon/siphon system is black and I had a look with a torch shining it through the water, but am not to sure what to look for. It did also mention that it was a SHIRES Syphon system. :?: