How do you house train a 5 year old dog?

The same way you house train a puppy. To start with, consistency is the key. Whenever he goes where he is supposed to, you give him praise. Every single time. When he goes somewhere he is not supposed to, and you catch him doing it, tell him no and then put him where he is supposed to go. Every single time. If you don't see him do it, you do nothing.Secondly, you need to watch him constantly for a while to make sure you can praise or correct his behavior as often as possible. If you can't watch him, put him somewhere where he can't get into any trouble (like in his crate for instance).

the same way i trained my puppy no different just older. for more specifics, go to your local library, and get a book on how to train your dog.