Bleach is the way to go if the tank is not actually set up.
The method used in nanoreefing4fun'd post will work well, but I'm more lazy. I'd just clean it all with fw, and then set it up and fill it with FW and add about 1 cup of bleach per 10 gal and let it all circulate overnight. Then make several full water changes, using only FW, about once a day, until you can't smell any bleach. Note that in this case we are using less bleach but letting it run longer.