Give it a few hot water soaks to remove tannin build up and let the wood swell to ensure no leaks. Then hit it with some room temp citric acid/ so2 mix water and let it soak for a few hours, drain and you should be good to go. Just don't let it dry out or else the wood could shrink and you would have a leaky barrel. Also probably the most important step would be to tell me where you got this barrel so I can buy one for myself!
