PROBLEM TO BE SOLVED: To discharge hot water in a bathtub by utilizing a circulation pipeline for re-heating.SOLUTION: A drainage system 12 includes: a heat source machine 14 in which a reheating outgoing pipe 16A and a reheating return pipe 16B of a circulation pipeline 16 for reheating are connected, and for heating hot water flowing in the reheating outgoing pipe from the reheating return pipe； a circulation port 20 provided in a bathtub 18, for supplying hot water from the reheating outgoing pipe 16A and for sucking the hot water in the bathtub in the reheating return pipe 16B； a circulation pump 42 provided at the heat source machine 14； a drainage pipeline 26 branched form the reheating outgoing pipe 16A and having a drain port 28 from which the hot water in the bathtub is discharged； and a three-way valve 30 provided at a branch part of the reheating outgoing pipe 16A and the drainage pipeline 26 and for switching between a normal flow path in which the hot water flows from the reheating outgoing pipe 16A to the circulation port 20, and a drainage path in which the hot water in the bathtub flows to the drainage pipeline via the circulation port and the reheating outgoing pipe or the hot water in the bathtub flows to the drainage pipeline via the reheating outgoing pipe from the circulation port and the reheating return pipe.SELECTED DRAWING: Figure 1【課題】追焚用の循環配管を利用して浴槽内の湯水を排出する。【解決手段】排水システム１２は、追焚用の循環配管１６の追焚往路管１６Ａと追焚復路管１６Ｂとが接続されると共に追焚復路管から追焚往路管に流れる湯水を加熱する熱源機１４と、浴槽１８内に設けられると共に追焚往路管１６Ａから湯水を供給し、浴槽内の湯水を追焚復路管１６Ｂに吸入する循環口２０と、熱源機１４に設けられた循環ポンプ４２と、追焚往路管１６Ａから分岐されると共に浴槽内の湯水が排出される排水口２８を備えた排水配管２６と、追焚往路管１６Ａと排水配管２６との分岐部に設けられ、湯水が追焚往路管１６Ａから循環口２０に流れる通常の流動経路と、浴槽内の湯水が循環口及び追焚往路管を介して排水配管に流れ、又は浴槽内の湯水が循環口及び追焚復路管から追焚往路管を介して排水配管に流れる排水経路とに切り替える三方弁３０と、を有する。【選択図】図１
