Am Freitag, 6. Oktober 2017 02:00:24 UTC+2 schrieb David Billington:

Items that are hot dip galvanised have to be vented in order to prevent
dangerous pressure build-up, I've had many items dipped and it is a good
processÂ* but theÂ* sections need to be vented to relieve the pressure
build up.

Makes sense. Not what I guessed, though. I was guessing it was to prevent stagnant water from building up inside the tubes and causing corrosion.