I would also not keep it cycled (and definitely not with a sacrificial fish). This won't work sometimes if you have to use the QT as a hospital, because many medications destroy beneficial bacteria.
I would either (1) keep an extra filter running on your main tank, or (2) just keep extra media inside your main tank or filter. You could transfer the extra media/filter over to the QT as needed, and break it down when you aren't using it. Another option would be to keep a sponge in your main tank, and rig a sponge filter whenever you need the Q.
I would always just toss out the filter media that's been in the QT and replace with new in the main tank, so that the new stuff starts building up its bacteria colony.
Oh, and a bit off-topic - the QT should be barebottom, but with a plant and a hiding place for the fish being homed.
I hope this information helps. :)