Its kind of like one of those steam toys they sell calling espresso machines.
Id say leave one valve cracked a bit, possibly the milk frother so it doesn't build up pressure and go boom, when it starts hissing let it rip, but if it is like one of the cheap espresso machines it should vent itself as it heats up and give you your water... id have to see it first hand to get a better idea. I have an old mr coffee espresso machine that is kind of almost similar..
Aaron