I bought a Fluidmaster 400UK077 toilet upgrade kit and successfully installed the float valve (in good time, since the old one fell apart as I was taking it out).
Unfortunately the "flapper" flush valve didn't work. I installed it but it didn't flush much and some water ran out between the cistern and the pan, so I had to reinstall the old syphonic flushing mechanism.
I noticed that the old mech had a small pipe centred within the water outlet. The small pipe ran partway up the last column (last in the direction of water flow) of the flusher, protruded about 3 cm from the outlet pipe, and had its own rubber seal onto a corresponding hole in the pan (inside the main hole). As far as I can tell it seems to be an aspirator that help the syphonic trap in the pan work.
Is it possible to adapt a modern flapper to work with a syphonic pan? Or am I stuck with syphon-flusher as long as I have this toilet?