To improve piping for a waste water treatment system capable of making a dental consultation room barrier-free.

In a waste water pipeline (a) between a dental chair unit 10 and an air-water separator 13, a merging unit 2 is disposed which is connected to a vacuum pipeline (b) and in which a float valve 21 which is floated on stagnating water in the waste water pipeline (a) connected to the chair unit 10 and a float valve seat 23 which facilitates the float valve 21 to float upside down is disposed. A switch circuit 27 or a hanger 5 associated with the switch is provided for automatically or manually opening an air valve switch 11 of a syringe at the end of the vacuum pipeline (b). A waste water outlet pipeline with an electro-magnetic valve 6 for the air-water separator 13 is connected to a waste water tank 3, which is connected to a compressed air pipeline (c) having an electro-magnetic valve 7 and includes a water level sensor 8 having a float 22, and which could also be provided possibly with an electro-magnetic valve 17 for discharging the waste water. A pipeline including a riser 9 without an enough gradient connects between the downstream side of a discharging pipeline and the existing discharging pipeline. It has thus become possible to store the waste water in the waste water tank 3 and to discharge the waste water by pressurizing, independently of the operation of the air-water separator 13.