When I go to a restaurant, I always check the rim of the glass I'm going to drink from before I start drinking.
Sometimes the lip of the glass is dirty, which means they didn't wash it well enough, so I never go back to eat at that restaurant again.
この場合、次のような言い方ができますよ。
ーWhen I go to a restaurant, I always check the rim of the glass I'm going to drink from before I start drinking.
「レストランに行くといつも飲む前にコップの飲むところを確認します」
the rim of the glass で「グラスの飲み口」と言えます。
ーSometimes the lip of the glass is dirty, which means they didn't wash it well enough, so I never go back to eat at that restaurant again.
「たまにコップの飲み口が汚れていると、コップをちゃんと洗っていないということなので、二度とそのレストランに行って食べることはありません」
the lip of the glass で「グラスの飲み口」と言えます。
ご参考まで！
カナダ 
