1
general::
Phrase(s): the bottom of the barrel [and] the bottom of the heap
Fig. the location of persons or things of the very lowest quality; someone or something of the lowest quality. (The fruit at the bottom of a barrel of apples is likely to be bruised from the weight of the other apples.) • That last secretary you sent me was really the bottom of the barrel. • I don’t need any candidates from the bottom of the heap.
McGrawhill's American Idioms And Phrasal Verbs
2
general::
The least desirable, the dregs, as in The nominating committee had trouble finding candidates; they were settling for the bottom of the barrel. The phrase often occurs in scrape the bottom of the barrel, meaning "to use the least desirable elements" (because one has no choice), as in Bringing up that minor legal point proves that you're scraping the bottom of the barrel. This metaphor for the sediment left by wine in a barrel was already used by Cicero to describe the lowest elements of Roman society. [First half of 1900s]
American Heritage Idioms