According to fire brigade officials, the tragic incident took place on a road in Sector 25. The deceased were identified as Kana Valmiki and Ajay Patel.
Chief Fire Officer Mahesh Modh said Patel, a cleaning contractor for main sewer line, had hired Valmiki and another person for the job.
"Valmiki descended into the sewer line through a manhole using a rope whose other end was held by the other worker from outside. Valmiki lost grip and fell. Patel, who could see Valmiki's hand, tried to help him but he too fell in. Both drowned before anyone could help them," Modh said.
Sector 21 police station have registered a case of accidental death and started further investigation.