A rusty sink drain is often caused by factors like rust, corrosion, and neglect. Rust occurs when metal components, such as the drain flange or drainpipe, come into contact with moisture and oxygen. This leads to the formation of iron oxide, a reddish-brown substance that can clog drains and create unsightly stains. To prevent and maintain a healthy drain, regular cleaning, drain protectors, water softening systems, and regular inspections are recommended. If rust stains persist, it is advisable to contact a plumber for professional assistance.