The overflow device for the tank which can assure the reduction of simplification and cost of structure is offered. This invention, although water W inside the tank is supplied to the external equipment outside the tank deals with the overflow device for the tank which supplies the water W of the external equipment inside the tank. As for this device, the influx side end is arranged inside the tank, the outflow side end is arranged outside the tank, water W inside the tank is led outside the tank and siphon pipe 55 of the opposite U letter condition which is supplied to the external equipment and the influx side end is arranged outside the tank, sending out water W from emission pipe 56 of the opposite U letter condition where the outflow side end is arranged inside the tank and the external equipment, it has with the water supply expedient which it flows into emission pipe 56 and the connected tube 8 which communicates between top of siphon pipe 55 and top of emission pipe 56. By the drive of water supply expedient, the occasion where water W is supplied to emission pipe 56, through connected tube 8 with the suction force which it occurs with the flow of water W, the inside of siphon pipe 55 is absorbed.構造の簡素化およびコストの削減を図ることができる水槽用オーバーフロー装置を提供する。本発明は、水槽内の水Wを水槽外の外部機器に供給する一方、外部機器の水Wを水槽内に供給する水槽用オーバーフロー装置を対象とする。本装置は、流入側端部が水槽内に配置され、流出側端部が水槽外に配置され、水槽内の水Wを水槽外に導いて外部機器に供給する逆U字状のサイフォンパイプ55と、流入側端部が水槽外部に配置され、流出側端部が水槽内部に配置された逆U字状の吐出パイプ56と、外部機器から水Wを送り出して、吐出パイプ56に流入させる送水手段と、サイフォンパイプ55の上部および吐出パイプ56の上部間を連通する連結チューブ8とを備える。送水手段の駆動によって、吐出パイプ56に水Wが供給された際に、水Wの流れで生じる吸引力によって連結チューブ8を介してサイフォンパイプ55内が吸引される。
