If you go to the final page of my Stuart series on the web Berra you will see a picture of the four engines that I have made, only the first one for the fun of it, the others to provide articles for the magazine.
You will see that I have only fitted taps to one off, that being the first, Since then I have omitted them to keep the costs down. Non of them have been run, perhaps one day I will find the time, and the confidence, to make a boiler, but that day never seems to arrive, Shame really.
Fortunately, those who know more about running them appear above to have answered your question.
Harold