My method of flushing the steam boiler is to open the water tap after I am done steaming and before I turn off the steam boiler. I run the steam/water until it stops (~210F), wait for the auto fill and turns off the boiler, leaving the brew boiler on.

I measured it and there's about 22oz going out.

I thought about this thread today when I did it, and it occurred to me that maybe I DON'T like that there is 22oz of cold water going into the hot boiler all at once. I don't like the rapid change in temperature on that metal and connectors. Maybe it would be better to do this by the end of the day or by the last cup. Turn the machine OFF, then open the steam boiler water tap to let those 22oz out, but no auto fill until the next morning when I turn it ON. Comments??

Quite often.

I use hot water from my steam boiler for a 500ml Thermos of tea each morning. The hot water tap on the Vivaldi is solenoid based. As soon as I'm done filling the thermos, I turn the steam boiler off, which also stops the refilling process. The machine is on a timer; when it gets turned on again, the steam boiler gets turned on also, filling itself with fresh water.

I also use it to preheat cups every morning / evening.

I also use the hot water tap from time to time for cooking.

The water then get flushed quite frequently.

As my steam boiler is made of copper (unplated) and as I wasn't able to find scientific evidence (yet) that drinking water daily from such a boiler would or not pose a long term health issues, I also do this flushing routine in a precautionary principle point of view.

For the same reason, I prefer to keep some scale in the boiler and to avoid doing unecessary descaling (first having a look inside the boiler every 6 months).