Re: expression of have a pee & going to bathroom.
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?"
I'm not a teacher, but I write for a living. Please don't ask me about 2nd conditionals, but I'm a safe bet for what reads well in (American) English.