take a slash 

British slang "to urinate".

"Dude, I'm dying to take a slash, but I can't find a bog."

take a slash by Soiled Undergarment August 13, 2003

take a slash 

analogous to "taking a piss". This phrase was used in the Season 3 Premiere of "Turn: Washington's Spies". Seems like a colloquialism of the late 1700s.

"Excuse me, I have to take a slash."

take a slash by BruinMBA June 18, 2017