This is the heater tap. Note: You will need the o ring (XB6203) when replacing the tap 1966-1977  Silver Shadow, T-series, Shadow II, T-2, Silver Wraith II  (VIN# 1001-26708) 

This is the heater return hose between the engine and the pipe that runs up to the heater matrix. 1977-1980  Shadow II, T-2, Silver Wraith II, Corniche, Camargue (VIN 30001-35411)

This is the heater return hose between the engine and the pipe that runs up to the heater matrix on the later. 1978 from VIN 35279 Continental, Corniche, Shadow II, Silver Wraith II, T2 onward