1. A toilet or toilet seat.
2. Comparing a toilet to the throne of a king or a queen, toilets being typically made out of porcelain.
1. At the office Jim like to announce he was taking a trip to the "porcelain throne" every time he had to take a dump.
2. Morning poops was the only time Steve had to himself for the entire day, he truly felt like a king on a porcelain throne.