Bhairulal Valmiki (35) and Dayaram Valmiki (53) were cleaning the 'baoli' (stepwell) yesterday in Arnod area when they fainted after inhaling the gas, they said.
Five others descended into the stepwell to rescue them but they too fainted.
"All of them were rescued and rushed to the district hospital where Bhairulal and Dayaram were declared brought dead," police said.
Two others have been referred to Udaipur district hospital while the remaining are being treated at a local hospital, they said, adding the body of the two men has been sent for post-mortem.