Also; push button cisterns have modern types of valve flush mechanisms, not a true syphon as used on all old w/cs before about 10 years ago when water regulations were changed to allow dual flush. Valve types suffer from leaking seals (constant trickle into pan - wasting water) which are often hard to find or unobtainable (i.e for derwent pacific), when they need replacing. You end up replacing the whole thing - £30 or so plus labour. Built in obsolescence! A traditional syphon £10 - will not usually fit & anyway requires a lever to operate - so you'd have to replace your 3 year old w/c! Trad syphons can now be adapted to variable flush - see interflush.co.uk
flowboy, August 2009