1. I need to go somewhere.
我要上厕所

2. I want to wash my hands.
我要去下洗手间
更含蓄的说法：
I need to powder my nose.

3. I need to answer the call of nature.
一种更为文雅的说法称内急为“the call of nature”，那么上厕所就成了“to answer the call of nature.”。
I need to make a pit stop
pit stop 是指在赛车过程中，赛车在途中紧急停留加油、维修的地方。看来，她们肯定将解决问题看作是一种“紧急维修”了。

4. I need to go pee.
我要去撒尿
I need to take a leak
I need to take a dump