chudford wrote:
Can anyone tell me where I can get replacements for the thin plastic
sheets in the syphon of a toilet cistern?
I have cut out plastic to replace them but they don't work so well as
the original.

Anywhere at all which sells plumbing bits, eg B&Q, Wickes, plumbers
merchants...

Though personally I've always just cut bits of heavy-duty polythene to
fit, without problems. If you buy a bespoke membrane you may well have
to cut that anyway (if that's your problem), as the cross-section
dimensions of syphons vary.

David