Here,the main advantage is that the foul sewer is flushed from time to time by part of the rainwater. However the serious disadvantage is that overflows are necessary on the foul sewer, causing possible pollution to watercourses.

• 半分流式的主要优点是污水管可以不断地被部分雨水冲洗,但它最大的缺点是污水管上必须设置排溢口,这可能引起水体的污染。