flushing has two distinct meanings.... one is for when you have gone over board on the nutes... whether it is salt locked or just the wrong ppms and all it means is to run about 4 times the amount of clean water through the pot than it can hold.... for instance if it was a 3 gallon pot you would pour 12 gallons of water through it.
the second kind, which is what you are asking about just means to water at the end of flowering with only clean water... no nutes... to make the taste be all it can be... flushing with juice or molasseses is very common since those arent things that will generally hurt the flavor or harm the smoker.
that is where the ambiguity in the answers comes from... to make it simple: last couple weeks, dont use chemicals in the water but water as normal.... up until a few days before harvest... you dont want them all full of water when drying time comes