This should have been in lesson #1
Never mind, too late ...
"Where is the bathroom" should be a valid answer. It ultimately means the same thing.
Does 'lavatory' not work?
latrina: until now it was Always called "bathroom" (in the anglo-saxon world the toilet), and now bathroom is suddenly wrong - toilet is now preferred. It's OK with me, but then we should be sure what is preferred.
the army calls bathrooms "latrines"