Sorry to hear about your girls! But yes in the case of a contagious disease you definitely want to disinfect the tank. Of course you'll have to re-cycle the tank before you put new fish in it, but that's the only downside.
There are a couple of ways to sanitize an empty tank, such as the use of boiling water, vinegar, or a mild bleach solution. I have only done the mild bleach solution after having a death from dropsy in my 10 gallon. You want to use a 1:19 solution, so I put in 19 cups of hot water and one cup of REGULAR (no dyes, detergents, etc.) Clorox bleach into the empty tank. I scrubbed the tank's walls and bottom with a paper towel.
You'll also need to sanitize all of the decorations, filter, and heater using your bleach solution, and also buy brand new filter media. Gravel may be harder to sanitize, so I would recommend just getting some new gravel.
After that, you rinse everything like crazy. Rinse, rinse, rinse, rinse, and then rinse again. Let the tank dry for about a day, then you can set it up again. When filling up the tank with water you can add double the amount of dechlorinator to the water. This will assure that all traces of bleach are gone and that you have absolutely no bacteria. Then, cycle the tank again and add your fish when it's ready to go!
Hope this helped, best of luck with your new guys. :)
Last edited by derpmeister; 06-28-2011 at 01:09 PM.