I fitted the same cistern about 18 months ago ill try to find fitting instructions and pass a guide to you but ill need some time to look, from memory i think the outer ring unscrews and the push button hooks round the floa inside , its quite a complicated set up inside not a normal syphon, bare with me ill try and get back to you, dont hold your breath too long though, regards Glyn.
glyn bowen
September 2007