1 general:: Urinate, as in Excuse me, I've got to take a leak. [Vulgar slang; c. 1930]
American Heritage Idioms
2 general:: Phrase(s): take a leak Inf. to urinate. (Crude. Use caution with the topic. Usually in reference to a male.) • I gotta go take a leak. Back in a minute. • He just went out to take a leak.
McGrawhill's American Idioms And Phrasal Verbs