Flushing With Water

We were fertilizing with crappy MG tomato stuff ( i know, i know, BAD idea)
...we have just bought good quality ferts.
some of our plants are just starting off in the flowering stage. we are wondering about flushing them with ONLY water before we start with the Bloom ferts.
will water work? we were @ the garden store and the guy there said you have to buy a flushing solution, as water alone will do nothing.
Is this true? or is this guy just a salesman?

you dont have to flush it now. just start adding blooming nutes. you flush two weeks before harvest so the plant uses up all its stored energy and you dont taste nutes when smoking. and when you flush you just use water. if you have a one gallon pot you use three gallons of water

Emily,
you didnt like the results form the MG tomato fert? I have used it on a few and had great results, used it really only in veg never in bloom though.