P K Sathi (53), her son P K Rejish (33) and another person V P Muneer (53) died of asphyxiation last evening while cleaning a septic tank, they said.
Muneer collapsed in the septic tank after inhaling toxic gas, following which Rejish rushed into it to save him. Seeing her son also collapsing, Sathi went inside the tank and she too met the same fate, police said.