dwarf gouramis are hardy fishes. I have 4 of em in an empty 8 gallon plastic container without filteration or aeriation watsoever. Just 50% water changes twice a week. and they will still survive (like their famous cousin, the siamese betta fighting fish). Just dont over populate them as they are very territorial fishes (and shy too).

My 2cent worth....

Wash the tank,filter, (and watever gravel/materials) thoroughly clean (disinfect it if u must). dry it out under the sun if possible. get a temporary container, fill in 1/2 with old tank water and 1/2 with new dechlorinated tap water. put your gouramis in their temp home for several days. Aeriate if u want (no need filter). Change 1/2 of the water with new dechlorinated tap water again after a day or two. if you wish, change 1/2 of the water again for the 3rd time after another couple of days. This is to let the gouramis to settle down in the new water chemistry. check the temp home for any signs of slimes... If all is ok, time to move back to old tank.

transfer 1/2 temp home water into the old tank and fill in the other 1/2 with dechlorinated tap water. and setup up the tank as you want. NOTE: you need to RECYCLE the tank all over again. Whether you want to use your gouramis or another sacrifiable fishes to do that dirty job, it is up to you. Change 1/2 the water twice a week to help the gouramis survive the cycle period. They should last longer than a week maybe a year 1/2 or two..