The phrase "knocks bottom out of" is used to describe a situation where something falls apart or fails completely. Its antonyms, on the other hand, are words that describe situations where something is successful or remains intact. Some possible antonyms for "knocks bottom out of" include "bolsters," "strengthens," "supports," "reinforces," "enhances," and "improves." Using any of these words in place of "knocks bottom out of" would give a reader or listener an entirely different understanding of the situation at hand. As with many phrases, it's important to understand the words' meanings to convey exactly what you mean.