In my case,with mini protank II, I just wash all the pieces in hot water and then refill it with another liquid. After 1 hour or so,old aroma is not present anymore. And right at the start,old aroma is very weak.
Now,another question is, will the new aroma be even stronger if I put it in whole new tank,probably... but ,for me,my way is just good enough.
And when I said ,I wash the tank,I mean,I wash just the tank,not the coil. About coil,I just remove cotton wick ,use some paper tissue to clean it a little,dry burn the coil a little and add new cotton wick. Simple as that.
To me,that's just enough,but for someone who tends to be perfectionist,maybe not.
So,I hope I help you a little.
Cheers.