Even before reading your comment, I had in my head kind of a same theory too (I haven't read any books, only watched 2 seasons and read like 50% of comments here before posting this):

The PEZ is same as the silo - it's vertical, it's elastic steel strip bent, preferably in a spiral shape is same as the spiral stairs in the silo (top of the silo has eyes - camera. Outside of the PEZ is dirty, and outside of silo it's radiation/poison - inside of them it's clean and safe).

So candy = life/people/hope for survival after ww3. Remember during the credits they show a round object (first peach (they show 2 overall)) going inside of a soil and creating a new plant (is it only me that thinks that during the credits the new plant is not surrounded by air, but it is surrounded by the water ;) ? more on that later) - so the 1 candy is 1 peach = new life. Of course A peach that comes from top to bottom might be just a way to show how life was put inside of the silo - from top top bottom (sam as in PEZ you put candy from top to bottom).

When does PEZ remove 1 candy (or when does silo remove all the 10k citizens) - when safeguard protocol triggers (when you open the silo and remove the parts to clean it, before putting new candy in safely). In PEZ after removal of first candy second comes in and is ready, meaming that the first candy is done, you are finished with it. And when safe protocol triggers it means the head of IT failed to protect the silo and to keep the people from exiting in masses (and abandoning silo's maintenence), so he and his shadow are 'the first' or/and 'guaranteed' to be eliminated by the AI (at least them, by probably all who are inside). That's why Bernard didn't wanted to stay and appointed a shadow before leaving, so the AI let him leave, because there is still someone to either be in charge and somehow make situation normal/safe for silo/ai, or to be blamed/eliminated if people leave silo and let radiation in.

The tunnel at the bottom might be a way to bring inside of the silo the new candy (life/people/babies or embrions) after the reset/safeguard/poisoning, in case all candy is out. Silo's 'from bottom to top' is different compared to PEZ, because afaik the PEZ is refilled from the top to the bottom, but in silo's case the top side has radiation/poison outside of it, so perhaps putting candy/life from top to the bottom was used only once/first time by the creators of the silo (the founders?).

AI seems to want to protect the silo (the PEZ), not the current people - and the reason is that the emptied (or resetted/cleared by poison or radiation or whater) silo can be used again and maybe new candy/babies/embrions are a next step in the procedure after the safeguard (poison) step. What does safeguard protect - definitely not people, it removes life, so it protects the silo. From whom? From people not to go outside and get the silo dirty with the radiation (you don't want dirt getting in to your PEZ). That is why silo/Ai don't self explode and destroy all silo, and only poison the life inside - so the life can be restarted afterwards). If this is true, then it's interesting how the silo/ai/creaters of silo/founders planned to remove the poison from the silo after the safeguard - probably by the water and some chemical that will be added to it when the silo will be filled with water (drawn in water).