In a previous sentence, "toilet" meant 厕所 ("bathroom" or "restroom"). This time, however, it should be translated as 马桶。
You're right that this can be 马桶、but in certain situations ("the restroom is out of order") 厕所 is correct.
In most situations, I'd say. It's euphemistic, in a sense, to put that instead of 马桶.
Why don't we need 用 here but we need it in 《手机我弟弟用坏了》？
In that sentence, the brother is not the thing that broke, so you can't say "弟弟坏了“. What the 弟弟 did was 用 (the 手机), and 坏了 was the result. In this sentence, the bathroom is the thing that broke, so you say 厕所坏了.