I generated octopus main body using generative AI and cut threads inside it in Fusion.

As frame of reference I used this model (inverted volume) to fit valve in the same way: https://www.printables.com/model/298195-multiple-styles-of-schrader-caps-tire-valve-cap-fo/files

Printed using PETG filament with model rotated upside-down using dynamic layers height and normal supports.