Mainline is considered the brand most “Preferred by the Pros.” We are so highly regarded because we know the industry. We are owned and operated by a plumbing, heating and industrial supply company that has been in business since 1858. Since 2006, Mainline has constantly innovated and adapted to market demand to introduce thousands of exceptionally valued, superior quality products. Every product undergoes rigorous testing and must meet stringent standards to bear the Mainline name. Mainline products are sold at many convenient locations throughout the U.S. and Canada.