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Phrase(s): Where can I wash up? [and] Is there some place I can wash up?
Euph. a way of asking where the toilet or bathroom is without referring to one’s need to use it. (Of course, this is also appropriate to ask where one can wash one’s hands.) • The minute he got to the house, he asked Fred, "Where can I wash up?" • Fred: Welcome. Come in. Bill: Oh, is there some place I can wash up?
McGrawhill's American Idioms And Phrasal Verbs