In article om,
"Dave Liquorice" writes:

As for a special cylinder not heard that one before, always assuming

It's a term that's used, just after the sharp intake of breath through
the teeth, to prepare you for being ripped off.

A friend in London needed a "special cylinder" as his wasn't a standard
size (more bull****). When it had been fitted, I worked out what was
special about it (in addition to the price of course); it has a strange
property of being able to pump boiling hot water round the coil for
ages without it giving up any heat to the water in the cylinder.
So, special meant it had been ripped out of someone else's house, and
has several inches of hard water scale encasing the coil, no doubt.

--
Andrew Gabriel