Splice the ventilation duct with the discharge and ventilation spout, The role of the CDVº and the subsidiary is to avoid disfonaje, and that the pressure of the atmosphere along with that of the discharges produces a rupture in the balance existing in the siphons of the toilets. For this, the ventilation channel (subsidiary) is used, which gives the system the connection to the four winds.0.050 m PVC ventilation duct.