Wherever heretofore any city of the third class shall have constructed any portion of its sewer system outside the territorial limits of such city by laying sewer pipes out from such city through a portion of a township and back into the city, the action of the city in so doing is hereby ratified, confirmed and made valid notwithstanding the fact that such action was not authorized by any act of Assembly in force at such time. And the section of the sewer system of such city so laid outside of its territorial limits shall be and remain a lawful sewer of such city in like manner as though it had been constructed pursuant to lawful authority.
53 P.S. § 39971