You don't want to plumb it together with your DT... that defeats the whole purpose. What to use depends on the fish's size and how often you'll be using the QT. Some people keep a QT running all the time with live rock (knowing that if certain meds are ever used, that rock will become QT-only). Most people use a few large PVC fittings to give the fish a hiding place and nothing else, running the tank off of a HOB filter and doing water changes to make up for the lack of biological filtration via live rock. Small fish are OK in a 10g (which I'd bet is the most popular size). I used a 29g most often, and have a 55g now so that I can QT anything I may want size-wise.
As for preparing it, just set it up with new SW, heater and filtration and then acclimate the fish just as you would going into your DT. If you aren't using live rock (particularly uncured LR) there is no cycle or such to be concerned with. Lights are not necessary and keeping the tank unlit is thought to help with the fish's stress level.
Edit: I should qualify what I said about plumbing with a DT... it can be done, but it has to be able to be isolated and self-sufficient when a fish goes in, and if there are no health issues it can be restored to sharing flow with the DT. However, if illness is detected and/or meds used it would need to be shut down and cleaned before reconnecting. You'd still need independent filtration etc. This system really only makes any sense IMO if you plan on keeping an always-up QT with live rock (which is replaced if copper meds are ever used).
