Newbie alert, please be gentle....

I have a WSPCL outboard with a steel tank
It's pretty rusty, so i'm looking to replace it with a brass one - Is this possible? If so, what model should I look for? Are they all interchangeable, or am I limited with my options? I notice my tank has two outlet on the underside - one plugged.
OR
What's the best chemical to use to clean up the current tank? If I can get it clean, then i'm happy to store the outboard with a full tank of juice when not in use to prevent it rusting up again.
Thanks in advance
Jon