PROBLEM TO BE SOLVED: To provide a water tank capable of notifying a user of a situation in the tank with a camera as needs arise without continuously installing a camera in the tank.SOLUTION: A biological treatment tank 1 includes a raw water inflow port 11 installed on a lower sidewall of a tower body 10, an aeration pipe 12 installed on a bottom part in the tower body 10, a pneumatic piping 13, a siphon breaking piping 13A connected to the intermediate of the aeration piping 13, strainers 14 and 14, a connection pipe 15 connecting the strainers 14, a treatment water take-out port 16 communicating with the inside of the connection pipe 15, a drain piping 17 extended up and down along an inner peripheral surface in the tower body 10, an injection pipe 18 of an aqueous solution of a defoaming agent installed up and down inside of the tower body 10, and a camera insertion pipe 19.SELECTED DRAWING: Figure 1【課題】槽内にカメラを継続して配置することなく、必要な場合に、槽内の状況をカメラによって知ることができる水槽を提供する。【解決手段】生物処理槽１は、塔体１０の下部側面に設けられた原水流入口１１と、塔体１０内の底部に設けられた散気管１２と、空気配管１３と、空気配管１３の途中に連なるサイホンブレーク用配管１３Ａと、ストレーナ１４，１４と、ストレーナ１４同士を接続する接続配管１５と、該接続配管１５内に連通する処理水取出口１６と、塔体１０の内周面に沿って上下方向に延在したドレン配管１７と、塔体１０内に上下方向に設けられた消泡剤水溶液の注入配管１８と、カメラ挿入管１９等を備えている。【選択図】図１
