The phrase "knocking bottom out" refers to removing or destroying the foundation or support of something. Its antonyms, or opposite meanings, might include "strengthening," "building up," or "reinforcing." By doing so, one could ensure that the foundation remained solid and could withstand any challenges or upheavals that might come its way. Other possible antonyms for "knocking bottom out" include "upholding," "supporting," "solidifying," and "enhancing." These words suggest a sense of stability, permanence, and reliability that is the opposite of the destructive force implied by "knocking bottom out.