Kannur (Kerala): Three persons, including a mother son duo, have been asphyxiated to death while cleaning a septic tank at a house in Pallipoyil, about 10 km from Kannur, police said on Wednesday.

P K Sathi (53), her son P K Rejish (33) and another person V P Muneer (53) died of asphyxiation on Tuesday evening while cleaning a septic tank, they said.