First of all, congrats on your new purchase! What do you plan on doing with the tank--aggressive fish, a super big reef, large peaceful fish...I'd love to know what your ideas are.
As for the cleaning, it'll be a bit difficult because the tank is so big. Now, when I was a senior in high school I took a science course where you had to maintain a mini-ecosystem throughout the school year. (This is where my friend and I got into saltwater
) At the end of the school year when it came time to clean the tanks, under her direction, we'd fill them all up with water and throw a cup or so of bleach in, mix it around, let it sit overnight, then scrub and rinse it
really well the next day. It worked for her for the fish tanks as well as the reptiles and amphibians, and she's been teaching that class for over 20 years.
Since your tank is so big, I'd suggest cleaning it outside. Fill it up with a garden hose and pour in a bunch of bleach, then let it sit and scrub and rinse it out thoroughly the next day.
Now the pet store where I work, we also clean our aquariums/terrariums/small animal cages with bleach, but we only fill the tank a few inches from the bottom, add bleach, and scrub it out and rinse well.
Whatever method you use, if you add any kind of cleaning product, just make sure you rinse it out really really well. Hope this helps!