汙水氣味

一個月前租客說樓上淋浴/衝廁所的時候有汙水氣味持續， 水管工看了說找不出原因，" nothing I can do about odor it wasn`t evident when we were there before but we checked what we could. " 剛才租客又發信息："the sever smell is sill happending periodcally. "  關於這個汙水氣味大家有好的建議嗎？