Stephen formulated the question :
BTW these kits: what do you reuse and what has to be replaced? Is the
can single use or can you use it to do more than one pipe before it
runs out?

You can maybe get away with more than one pipe, but not to be relied
upon unless it is designed for more than one pipe. Basically you throw
the whole lot away and get a new kit - unless it is a commercial kit
which is refillable/expensive. You can also buy/hire electric freezers.

Using one takes some confidence in both the kit and your ability to get
the job done before the ice plug melts. They also only work where there
is no flow at all.

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Regards,
Harry (M1BYT) (L)
http://www.ukradioamateur.co.uk