Abarim Publications' online Biblical Hebrew Dictionary
There are two root-verbs of the form בקק (baqaq), which at first sight don't seem to have anything to do with each other, but at closer look appear not all that far removed. One of the two is closely related to the root בוק (bwq):
The root-verb בקק (baqaq I) means to be empty but is used most for lands and countries stripped of people and produce (Isaiah 24:1, Jeremiah 51:2).
Originally, this verb may have to do with an Arabic verb meaning to make a gurgling sound. That would explain this verb's derivation: the masculine noun בקבק (baqbuq), meaning flask (Jeremiah 19:10). Perhaps (and this is a wild guess) this word typically denotes not so much a storage vessel, such as a jar, but rather a flask that was designated for continuous use, like a carrier flask; one that was filled at some point and then slowly emptied during a process of usage.
Then there's the second verb בקק (baqaq II), which is used only once, in Hosea 10:1, where it appears to mean to be luxuriant. Scholars assume that this version of בקק (baqaq) is related to an Arabic verb that means to be profuse or abundant. Obviously, a carrier flask has no purpose when there's nothing to fill it with, and perhaps carrying one could be interpreted as having abundance of whatever the flask contains.
From the verb בקק (baqaq I) it's a very small linguistic step to the by-form בוק (bwq), from whence come the feminine nouns בוקה (buqa), and מבוקה (mebuqa), both meaning emptiness and both only used in Nahum 2:11 (these two words relate like emptiness and emptihood).