I keep hospital and quarantine tanks completely separate from each other, Both of the tanks are old 2'x1' ones bought cheaply from Ebay, both tanks are kept completely separate and never mixed.
The quarantine tank is filled when needed from my main aquarium,
it has minimum rocks a couple of fern plants and 2 plastic tubes as hiding places, I run an old canister filter.
I keep all of new fish for a minimum of 21 days in quarantine.
The hospital tank is usually half full of water taken from my any aquarium (but not from the aquarium the sick fish came from) basic filtration, airstone, fern and 2 plastic tubes that the fish can hide in.
When the fish have been treated, they are moved to the Quarantine tank and treated as new fish, both tanks are completely disenfected between uses, when moving the fish from hospital to quarantine tank use a bag of main aquarium water to move the fish, this minimises cross contamination between tanks.
At least you are suplying a tank for to attempt to keep your main tanks free of nastys.
I can't really stress the importance of having spare tanks for emergencies.
By the way using water from a main aquarium stops the need for recycling.
Hope this helps someone to manage hospital or quaranntine tanks.