There was a story regarding Dudley's hippo who was named Hercules, I stand to be corrected but I think Dudley took him in as the place where he came from was shut down and the hippo would be put to sleep.
He lived where the gibbons are now, if you look inside the gibbons house you can see the steps at the front which led into a little indoor pool,he also had an outside pool.
I don't think he lived too long at Dudley as he was pretty old when he arrived, and I guess this must be about 12 to 15 years ago.