That depends whether you are using ‘Side Stream’ or ‘Mainstream’ Capnography.
Side Stream : A T Shaped Connector is used to carry the gas samples pumped from the patient to the CO2 sensor in the main unit, away from the airway.
Main Stream : A airway adapter is used inserted straight between the ET tube and breathing circuit and the sensor is just connected to that.
Main Stream is used when you need to see real time ETCO2 measurements, but needs to remain heated and can get blocked by saliva etc. Side Stream are easier to connect and are helpful when the patient is in an awkward position, but CO2 measurements are not always accurate.
Hope this helps!!