My understanding is that there is a boiler filled with water with these machines. If you don't use the machine over the weekend do you put through a batch of water without grounds to get rid of the stale water?
If I leave it set for an extended period I will run 2 full 72oz of water through to flush. The boiler is 1.5 times the size of the end brew so 2 through will exchange all in the boiler.
The machine does not need to be turned on to do this. There is no pump. The inflow displaces and forces the hot water to the brew head. Just make sure the basket and carafe is on the machine before you start otherwise it can make a real mess (no way to stop it once it starts... Don't ask.. it wasn't pretty).