The incident took place yesterday in a private housing society in Isasani area of South-Western part of Nagpur.
According to police, the sanitary workers were unaware of the presence of toxic gas and entered the chamber to clean the chocked drain and died due to suffocation.
The victims were identified as Sunil Nekram Walmik, his son Rinki, Sumit Dinesh Walmik and Balu Namdev Masate, they said.
Another worker identified as Pramod Chavan was rushed to a nearby hospital in a serious condition.