第一句：I need to go somewhere.

我需要去趙洗手间。

A: Would you mind I leave for a moment? I need to go somewhere.

您介意我离开一会儿吗？我需要去趟洗手间。

B: Go ahead.

请便！

第二句：I want to wash my hands.

我想去趟洗手间

A: Excuse me. I want to wash my hands.

对不起，我想去趟洗手间。

B: As you like.

请便！

其他表达法：

Where can I wash my hands?

请问洗手间在哪里？

Could you tell me where I can wash my hands?

请问洗手间怎么走？