Hello,
when there is NO Drainagevalve the water can not go through the brewgroup.
The hose which goes into the Drainagevalve is also the one who brings the fresh, clear hot water from the valve near the heatingelement. When teh Drainagevalve is closed, the water goes through the brewgroup and makes the coffee. For a dry waste, the drainagevalve opens after the brewing and lets the water flow out and air in, so the wate gets out easy and isnt very wet. the drainagevalve is switched by an electric magnet, it mmakes a loud click noise.
[guide|15942]
in this link: the hose brings fresh hot clean water,
in picture ONE the part in the white circle lets the water into the brewgroup dock.
The side where you can see the spring is the middlewall, behind that wall is the elctric magnet. sorry for my bad english, was not best at school. XD