My QT tank is a little 20 Gallon tank, with a small filter an heater an air line and some PVC Pipe0s and elbows. I store it under a cabinet when not used. When I get an itch for a fish, I start it up with water change water then I take a piece of sponge or filter floss that I have in the tank and stick it in the QT filter and its ready to go. I've set it up litterally 24 hours before I bought a fish before, with no problems.
Others may have better input..