From Longman Dictionary of Contemporary Englishtake/have a leaktake/have a leakinformalHBH to get rid of waste liquid from your body SYN urinate → leak
Examples from the Corpus
take/have a leak• Billy got off his lounge chair now, went into the bathroom and took a leak.• She locked herself into a cubicle and took a leak.• Well, rumors have leaked out.• Cully goes off to take a leak.• Tank owners are required to have leak detection equipment installed by December 1993.• I'd gone behind the set to take a leak and I heard this sound like snapping wood.• I thought it was a damn silly place to park if some one wanted to take a leak in the bushes. 