A tea pet is a small unglazed clay figure kept on the tea tray. The practice is to pour the rinse water over it as you brew; because the clay is porous and unglazed, it absorbs tea oils and gradually darkens and polishes. The figure is a companion to the ritual, not a functional vessel.
Yixing clay — zisha — is a stoneware clay from Jiangsu with a high iron content, fired but never glazed. Because it is unglazed, it will stain: that is expected, and long-term tea drinkers consider it the point. New pieces should be rinsed in plain hot water before first use and never put in a dishwasher.