Drainage
Drainage Ditch, Gutter
noun
You already know that emitted water means "drainage." Add gutter to that and this becomes a drainage in the sense of a drainage ditch or gutter.
When it comes to the drain in your sink or bathtub, you can use 排水口, which has the same pronunciation but a different kanji.
This is a jukugo word that uses the on'yomi readings of the kanji. You should be able to read this on your own.
排水溝に落ちて怪我をした。
I fell into a drainage ditch and got injured.
排水溝と排水口がごっちゃになってる人って日本人でも結構多いよね。
It's pretty common for even Japanese people to mix up 排水溝 and 排水口, isn't it?
詰まると大変だから、側溝や排水溝は定期的に掃除しておいた方がいいですよ。
It's important to clean the gutters and drainage ditches regularly because it can be a big hassle when they get clogged.