If its an old one you might just as well replace the syphon in the cistern, as you have to remove the old one to put a new diaphragm in anyway.
Fixing depends on type of toilet. low flush or close coupled. low flush less work.
1. Turn off the water feed to cistern.
2. If you can get it to flush flush to drain cistern mop out residue water.
3. remove flush tube from cistern to pan to access the large plastic collar under the cistern holding the syphon in place.
4.remove this threadeed collar and remove the syphon (You may have to remove float ball from float arm )then replace with new syphon.
Close coupled requires removal of cistern from toilet. 1. Turn off water and drain cistern as above.
2. Remove the water feed pipe from cistern.
3. Remove screws holding cistern to wall.[if any at back inside cistern]
4. Remove the cistern to pan bolts lift cistern clear of pan.
5. Turn cistern bottom up remove the threaded plastic nut to remove syphon. Replacement isi revers but also replace bolts and the large doughnut size seal between pan and cistern you can buy a full kit, bolts plate and doughnut seal.
Bob, June 2009
