*Rusted Compressor Tank*
No.1 Reason Not to use a compressor tank that has surface rust or any type of rust on it.
Photos speak louder then words!!
If you see rust on the outside of your compressor tank, there is a very good chance the rust has started for the inside of the tank and come through to the outside of the tank. It is best either to have your tank inspected and tested or just replace the tank.
Remember safety 1st.