Hospital tank, or quarantine tank for newly aquired fish as well, is pretty simple to set up. It doesn't even have to be a tank, a properly sized rubbermaid container (10 -15 gl per fish) will do just fine.
All you need is a filter for that tank, and it can simply be some filter media taken out from an existing tank (preferably of course not a tank that has sick fish in it for obvious reasons
), and put that media in a spare filter. Then there is an airstone, run by an airpump, as well as a fake plant or two for the fish to feel comfortable and have some hiding spaces when he doesn't feel well. A heater is also a big help to keep the temperature stable, and even better to raise the temp a bit around 78-80 degrees. In a temperature like that the life cycle of most parasites will speed up, which means the treatment time is shortened.
Thats the basics...I wouldn't put any lights on a hospital tank, since sick fish are generally stressed, and have a more quiet time in a dark tank, which by the way is very suitable for a lot of parasites anyway, since they multiply more in a lighted tank.
I have never started a hospitalization tank before and I want to go ahead and set it up so that it will be available if something happens. (Hope that it doesn't) I currently have a fish that is not doing so well 
but he is in his on tank already so I am just treating him in that but I have an assortment of other orrandas and I just want it for back up. What do I need to do and If I fix it up and one gets sick, when they are better how do I re-sanitize the tank. 