Im getting a red eared slider, help?!?

MY friends Autistic brother decided he hated his turtle and refuses to feed or water him, so of course im going to take him. Only problem is ive never owned one, ive looked up how to care for them, but i am low on money so can i temporarily keep him in the bathtub? Or maybe put something together out back as i live in Arizon? It would be temporary until i get funds for a permanent habitat. Anyways give me your insight!