Do I need to unscrew the bottom of the S-bottle during feeding?
No, the bottom should not be loosened, but rather tightened hand-tight.
If the nipple creates a vacuum, it indicates that the anti-colic valve at the bottom of the S-bottle is not functioning properly. Therefore, always check before each use that the air hole in the anti-colic valve is open by gently squeezing it. See: How do I open the valve at the bottom of the S-bottle?
