Since the beneficial bacteria live in the filter, not the water, you *shouldn't* need to cycle the tank again if you're just giving it a new "look." If you're doing a total scrub-down, getting new gravel, etc., and you want to totally empty the tank, either run your filter on another tank and take as long as you need to clean the old tank, or put the filter (media) in a bucket full of old tank water, work quickly, and get the filter running again in the new (dechlorinated) water/tank. (or, depending what kind of filter you have, put it in the bucket and plug it back in. Then you don't have to worry about the bacteria dying off).