Help what siphon do I need.

[MikeSharp01]

A friend has a problem with her flush, no pun intended, and I need to get a new siphon. What one do I need there seem to be various sizes none of which tie up directly with the dimensions of the existing unit. See pic any ideas and can I get new tank to pan studs as these are so rusted that I may have to saw them off. Any pointers as only got time for one trip to screwys and an hour to fix. 

[PeterW]

Cistern has to come off to fit that anyway so water off, pull the syphon out and measure the hole. Quicker these days to convert to a push button flush too - goes in the handle hole nice and neat. 

[Vijay]

I changed to a push fitting as Peter suggested, one of these in fact https://www.diy.com/departments/fluidmaster-red-chrome-effect-plastic-toilet-flapper-valve-complete-with-push-button-kit/211927_BQ.prd

[MikeSharp01]

2 hours ago, PeterW said:

Cistern has to come off to fit that anyway so water off, pull the syphon out and measure the hole. Quicker these days to convert to a push button flush too - goes in the handle hole nice and neat. 

Done it thanks both got it apart with a hacksaw on rusty bolts just back from getting cistern no B&Q local but there was a diddy little plumbers merchant. will fit after lunch.

[Danny68]

Another option for anyone else doing this  is to buy a 3 part syphon, you can pick them up for a less than a tenner, that way it makes servicing in the future a 3 minute job, and it will only cost a £1 for a new syphon washer.