That`s a reasonable call - out charge Drops to £40 when the syphon is paid for . I`d have fitted a drop valve which costs more - Infact i did just that and a new float valve for a family member recently and the bits cost £20+ . IT`s a viscious circle - there is no money in jobbing Plumbing - it`s all with the boiler fixers . And there is less old school plumbers about - in 10 years we won`t even be here bothering to reply to DIY`ers for free ... Get a new Bog in - £ 60 in a box to carry home from a DIY shed