You should just come clean, he's gonna notice a new tank, since it'll be a slightly different color without the fuel stains on it and scratches from use. no sense in hiding it, so take responsiblity for your own actions. sooner or later he'll find out, and then he'll be even more pissed off with you when he does find out. tell him you broke it, and are replacing the parts you broke now, it'll make life MUCH better for you.
Sorry for the lecture, its just how I have always felt, and always will feel. when you lie, it'll come back to bite you on the a$$ sooner or later no matter how good a lie you tell.