You will have to change the drain mechanism where the water runs out, because most bathtubs slowly let water out, and that could be a pain. Maybe seal it closed, or use it as a bottom drain. I used to put my fish in a tub in my garage. Same situation as you where it was an extra tub, we used it to hold the fish when we were working on the pond, and we also used it to bath the dog:-)

I am not sure about the tub surviving the winters in Ohio. Is it porcelain? I would bury it for looks sake, so it does not look like a big tub. Or, what we did is keep it it above ground on cement, and piled garden cement stones around it to make it look nice. But, it should not be necessary to bury, as bathtubs are meant to be above ground.

i was gonna put a liner in it,,jus gonna use it more for it's shape,,,an was gonna put it against my foundation on one side,,then put something on other side so that would help protect it some more,,,,let me know if anybody comes up with any more ideas