| CPC F04F 10/02 (2013.01) [A01K 63/047 (2013.01)] | 14 Claims |

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1. A drainage device provided inside a water tank, and including a siphon mechanism formed of a siphon pipe and a cylindrical portion, the drainage device comprising:
the siphon pipe including a first opening an upper portion of which is opened on one end side, and including a first connection portion connected to an overflow pipe on the other end side; and
the cylindrical portion having an inner diameter larger than the siphon pipe, and having a second opening a lower portion of which is opened and into which the first opening of the siphon pipe is inserted, the second opening set in a position lower than the first opening,
wherein a second connection portion for selectively connecting an inside of the cylindrical portion to an air supply unit or atmosphere is provided on an upper surface of the cylindrical portion.
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