For me, any empty tank is a hospital tank or quarantine tank. I will add a bit of bleach to clean the tank after I use it as a hospital tank if necessary, depending on the nature of the disease I'm trying to treat. My hospital tank has no substrate, only a simple sponge filter. Very easy to clean.
However, from experience, I have very limited success with curing fishes. It's often easier to just provide a place for it's final moments.
Cheers,
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