There is no purge valve to bleed air from the system and not needed. Once you change the coolant, empty and refill the reservoir and drive the car as normal. Air in the system will burp out the reservoir over a couple of days, just check to see if you need to refill the reservoir.
So what? You say the gas engine dont need to have bleeders and diesel yes? Your water pump is ready to works with a lot of bubles and empty of fluid some parts of the circuit until the system bleeds himself? Uff, i think is not a good idea not have this cheap and simple part to bleed the circuit without do work the pump in this condition, if the Honda engineers dont put that in gas engines...ok best for you, i guess