Fixing a button flush with concealed cystern?

I have a button flush (one button for large flush and one for small) and it seems to have stopped working. The removable plate with the buttons on, has a tube connected which blows air when pressing the buttons which i assume rasies the stop-cock, however this tube is not connected to anything and i can only assume it has become detached from something. When looking into the cystern (which is difficult because it is concealed) i cannot see where it should be connected, anyone any ideas?? your help would be much appreciated.