knock the bottom out

(of something)

1. and knock the bottom out Lit. to break the bottom of a container. I knocked the bottom out of the barrel and used it to store compost. Knock out the bottom and set it right on the soil.

2. Fig. [for something] to go down so low as to knock out the bottom. The bad news knocked the bottom out of the stock market. The recession knocked the bottom out of our profits.