In the United States, the more polite terms I hear are usually either *the restroom* or *the ladies' room*/*men's room* (always including *room*). *Washroom* sounds Canadian to me. British terminology (such as *loo*) may well be understood but would sound odd.

So, I might ask: "Where's the restroom?" If I already knew, I'd most likely excuse myself without explanation.

**BEWARE:** In the United States, using the word *toilet* to mean anything other than the actual porcelain fixture sounds shocking or rude. The difference between British and American English in this regard is quite pronounced. The first time I visited the UK, I was quite surprised to see signs which read "Toilet." You would never see such in the US.

Also, I've encountered people in the UK who don't understand the word *restroom,* which is usual in the US. So, even within English, there's significant variation from region to region.