Is phrase " take a dump" common used in AmE? or there are other good expression?The verb in AmE is to piss. (Vulgar)
Also common is to take a leak.
I suggest that both "take a dump" and anything involving the word "crap" would be considered at least moderately vulgar.
As a cultural note, Americans tend not to talk about this at all. If you were with a friend and had do this, you wouldn't say so. You'd say something like "I need to use the restroom" or simply "Would you excuse me for a moment?"
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