In message , Mark Brader
writes

A "pipe" is once through the tunnel (the main one, the Southgate tunnel
doesn't count), so a typical 4 pipe turn would be one that does pick up
Arnos east and do CK HR123 CK AGw, get off and have grub then
pick up Arnos west and do UX CK AGw, get off and finish. ...

Interesting usage! Do staff on other lines use "pipe" this way?
The Piccadilly isn't the only one with a central tunnel and open-air
sections at both ends (okay, near both ends), but not all are like that --
does this affect the usage?

Dunno, never been on other lines, but I'll ask the question.

Is "pipe" also used for the main tunnel itself -- would you say something
like "I was driving east and it failed 15 seconds after I drove into
the pipe" and expect people to know exactly where you were?

Generally, yes. On the Picc., a pipe is about 40 mins and we do talk in
pipes - sad but true. 'The pipe' for us is the main Arnos - Barons
Court section - other bits don't count.
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