You can use a solution of 1 part bleach to 19 parts of water to wash your tank. After that you have to rinse with (hot) water allot! Just to make sure you don't have anymore bleach in there. Decor the same thing, and gravel.........well, i would boil, but i'm thinking letting it sit in a bucket with very hot water for 15-20 minutes should kill most of the bacteria/parasites that are present.
What happened that you need to sterilize everything?