What it means
Where is the toilet? 洗手间 is the polite word — literally "hand-washing room."
When to use it
卫生间 and 厕所 also work; 厕所 is more blunt. In an emergency, 洗手间 is the safest choice in a restaurant or mall.
Examples
qǐng请wèn问，xǐ洗shǒu手jiān间zài在nǎ哪lǐ里？
Excuse me, where is the restroom?
xǐ洗shǒu手jiān间zài在èr二lóu楼。
The restroom is on the second floor.
zhè这lǐ里yǒu有xǐ洗shǒu手jiān间ma吗？
Is there a restroom here?
The full set of survival phrases for greetings, dining, shopping, and getting around, each with audio.