...Google has the answer! According to Wikipeadia "Threading a 22mm pipe and feeding it down cavity wall"...
Probably all sat in an office using their employer's time and internet connection to find a way of saving a few quid because they are too tight and stupid to pay for a proper job.
Hmmm...would any sensible RGI put a run of pipe into service that he hadn't fitted himself and then put his name to it, whether it passed its tightness test or not??
Can't say I know of any!!
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