Painting a tank is not something that we recommend but we know that it is frequently done. Once painted, the tank would not be covered under our normal warranty. Based on what distributors and customers have told us, to prepare the tank for painting, wipe it down with a paint thinner to remove any oily residue. The paint that seems to adhere the best is an automotive urethane which is commonly used to paint car bumpers. Keep in mind that over time, as a tank expands and contracts, the paint will usually crack and will need to be reapplied.

Source: FAQs - Peabody