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Filth.
I use boiling water, with a high heat at first.
Once the coffee starts to come through, I turn the heat right down.
Once the coffee coming out starts looking frothy, I take it off the heat and put the base into a pan of cold water to stop if over-extracting.
If I forget (or if my otherwise perfect wife makes the coffee), the whole lot starts spaffing everywhere and also turns into a bitter swill.
It starts gently and then ends in a gusher.
;-)