Introduction: The cause of incapacitation of sewage cleaning worker (B) in the septic tank related to toxic gas presence. Case Report/Description: B went into the tank with his co-worker (C) after they noticed the first co-worker (A) that went in taking a longer time than usual. The last three co-workers (D, E, F) experienced breathing difficulty after they enter the sewage tank, E and F managed to come out from the tank while A, B, C and D collapsed in the tank. Autopsy revealed a man with his belonging soaked with fluid and stains with sludge, emits rotten eggs-like odor. The conjunctivae and tongue were stains with sludge. The upper airways and trachea were filled with sludge. The lungs appeared hyperinflated and heavy, cut sections showed edema with sludge filled up to distal airways. Presence of dimethyl sulfide (DS) in lung tissue, and dimethyl disulfide (DD) in blood and lung tissue. Histological examination of lungs showed edematous fluid filled the intra-alveolar space with foreign bodies seen. Discussion/Conclusion: Septic tanks are enclosed areas made for accumulation of decomposed domestic wastes, sewerage and its resultant gases. Decaying organic matter releases toxic gases including hydrogen sulfide (H2S), ammonia, methane, and carbon dioxide, as well as carbon monoxide. DS and DD are the by-product of H2S. Autopsy findings in cases of H2S poisoning were non-specific. In this case, toxic gas inhalation causing incapacitation in the sewage tank which lead to sludge aspiration was undeniable. The cause of death was concluded to be septic tank related death.