Also, isn't plumbing a technology? Or does it have to be in the Civ VI Technology tree to be recognised as one?
I know Agriculture and Animal Husbandry is
Most scientific and engineering skills would also be useless if civilization collapses. For example, I am a scientific software developer. Most of my work has been for medical research, which is something people tend to respect. However, I wouldn't be able to do anything useful with numerical modelling in a survival situation. My limited skills as an amateur home renovator would be far more relevant.
It's a bit like Maslows hierarchy of needs. First we need food and water and plumbing. When we are secure in those needs, society can take the next step. But the basis of security must be there before advancement
I would say we need hygiene, which is different than plumbing. Plumbing comes into play when we have cities large enough that we can't rely on outhouses.
To be fair, most professions that would be needed to survive in an apocalypse or rebuild society, aren't things that an already functioning modern society can support everyone doing anyway. We need farmers and carpenters and such, but we don't need so many as to have openings for a majority of the population to be them, these days.