The deceased were identified as Babu (20),Nayan Singh (28) and Kanihya alias Kansingh.
The bodies were sent for postmortem in Pushkar's civil hospital, they said.
Around mid noon, Babu had stepped into the sewer chamber but he got suffocated and fell unconscious inside it probably due to poisonous gas, they said.
To provide him helping hand Nayan went inside, and then Kanihya tried, but they all collapsed there, police said.
Three were rushed to the city hospital where they were declared brought dead.