Job done. I got one out with WD40 but had to hacksaw the other off and - of course - it was on the most restricted side!

Got it all apart and off to the merchants tomorrow for another siphon. This bathroom is overdue for renewal so I'm gonna stick the cheapest I can find in for the time being - the suite was only a cheapy but 19 years on it looks fine and this is the first trouble it has given.

And why can't someone invent nylon fittings or something else that won't rust up, either for cisterns, or toilet seats? I'm now positive that there's a market for this...