You could rinse it with hot water [ as hot as you can stand ] .Then when the tank is empty , no water in it , you can wipe it with either rubbing alcohol or clear amonia , not scented or soapy . then rinse it again well with clean water and let it dry. I myself don't bother any more . I keep my quarentine tank running always , I also try to keep something living in it plants , malayian snails , shrimp , anything to keep the nitrifying bacteria alive . If , if a fish becomes ill I usually treat first by changing water if that doesn't work I go for meds that are safest for plants and bacteria , and hopefulywill cure my pet . If something stronger is needed I isolate the fish to a hospital tank . If your talking about small fish here 2 10 gal tanks should be good . I believe there is a differnce between a quarentine tank [ new healthy arrivals min 2.5 weeks to 1 month ] and a hopital tank[fish that become ill for whatever reason ].This is my opinion others may disagree .You don't necessarily need the gravel in either Ken . sorry for rambling