your/somebody's number two

number two

1. One's second-in-command; the person with the second-highest level of power or authority in some group, company, or organization. He left his number two in charge while he traveled abroad to seek new investors. This promotion will actually make me the new number two in the company.
2. euphemism Defecation ("number one" being a euphemism for urination). Do you have to do a number one or a number two?
See also: number, two
Farlex Dictionary of Idioms.

your/somebody’s number ˈtwo

(informal) the second most important person in a company, an organization, etc: Brian Jones is the new number two at the ministry.
See also: number, two
Farlex Partner Idioms Dictionary

number two

n. defecation; an act of defecation. Mommy! I gotta do a number two.
See also: number, two
McGraw-Hill's Dictionary of American Slang and Colloquial Expressions
See also:
  • number two
  • in (just) a second
  • in a second
  • a second thought
  • any second now
  • any second
  • second bite of the apple
  • second go
  • split second
  • a split second