The phrase "knocking the bottom out of" is typically used to describe actions that result in the collapse or destruction of something. Antonyms for this phrase may include "building up," "strengthening," or "reinforcing." These terms indicate actions that add support or stability to an object or structure, rather than weakening or destroying it. Other antonyms for "knocking the bottom out of" might include "preserving," "conserving," or "maintaining," which suggest efforts to keep something in its original, intact state. Overall, antonyms for this phrase tend to focus on positive actions that protect, sustain, or enhance, rather than negative actions that undermine or destroy.