A compensating tank for a hydraulic motor vehicle brake system, having a housing including a housing upper part and a housing lower part and having a device for monitoring the tank filling level of the compensating tank, including a switching unit, which is welded to the housing and has a plug connector, and including a sensor or switching element which can be switched by a transducer at a switching point S at which the switching unit generates a signal for an electronic control unit. The housing has a depression for holding the switching unit, with the switching unit having a base body composed of plastic, which base body is welded to the housing in the depression, and with the depression being provided such that the base body of the switching unit forms a planar surface with the housing.