The former Economy Plumbing & Heating Supply Co. building at 3190 Washington St. (Gazette Photo by Rebeca Oliveira) EGLESTON SQ.—A block of Washington Street that includes former plumbing company and car garage is being eyed for an energy-efficient, mixed-use development. Developers Dan Mangiacotti and Paul Iantosca are looking to redevelop the 3190-3204 block of Washington…