I do the same... drain, temp match, add prime, fill. But... 8 drops isn't going to cut it. It would probably just be easier to add most of a cap full... you gotta use prime (or any de-chlor for that matter) for the volume of the tank, not the amount of water youre adding.
"What, exactly, is the internet? Basically it is a global network exchanging digitized data in such a way that any computer, anywhere, that is equipped with a device called a 'modem', can make a noise like a duck choking on a kazoo." - Dave Barry