You could add bleach to the tank and let it soak and then neutralize the bleach with lots of dechlorinator. Do several water changes and then rerinse again with extra dechlorinator. You will have to test the final water to be sure the chlorine and chloramines have been neutralized. You'd also have to be careful not to spill the bleach on anything. It can be done. If you lived close by, I'd give you a hand.