I don't keep one set up all the time...
I keep a 20 tall around for emergency wound/infection treatment, actually quarantining a true parrot I recently bought in there now.
I'm not a huge fan of sponge filters so I keep an extra HOB around just for this tank, as well as an additional heater (note: these are for this tank only).
Simplying adding some established media to the hob, ie: extra sponges and bio-max from a currently running well established tank. Should, (depending on the amount of media and the size/load of the established tank) be enough to stabilize a small quarantine tank. Transfering the media as well as condtioning the new water should have you up and running in about an hour; I've done this a few times before, so it may take longer the first few times you do it. Make sure and test the water once it has been running and gotten to temp. to avoid the dreaded new tank syndrome.
As far as cleaning the equipment, I would suggest steaming hot water and plenty of dry time. You shouldn't be adding anything that you used in your quarantine tank back to your display tank except maybe for the biomax you've taken out of one of your main filters, again, hot water and plenty of dry time will be required before adding this back to your main tank.
As long as your able to keep some extra, cheap sponges as well an extra bag of biomax or something like it running in your main tank, you should always be ready to set up a quarantine tank.
Good luck
