To easily surely and quickly clear a clogged filtration layer in a septic tank.

The subject cleaning apparatus is provided with the septic tank 1 in which a filter medium 2 is packed for treating supplied original water, an air lift pipe 5 arranged vertically in the septic tank 1 for lifting a mixture of the medium 2 sucked from the bottom side of the septic tank 1 with a part of the treated water by the action of the air introduced through an air pipe 16 and a separation unit 9 for separating the medium 2 from the mixture discharged from the upper end of the air lift pipe 5 and returning the separated medium 2 to the septic tank 1. A stop valve 17 is arranged on the air lift pipe 5 for closing the pipe 5 when the filtration layer formed by the medium 2 is clogged.

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