In Oakland Co Drain Comm'r v. Royal Oak, 306 Mich 124, 145; 10 NW2d 435 (1943), the Supreme Court of Michigan held that the City of Detroit's grant to Oakland County of the right to construct a connecting sewer under a street within the city limits did not constitute a franchise, but was merely a right incidental to the principal purposes of the two contracts between the county and city. To carry out such principal purpose, which was the transmission of the district's sewage to the Detroit treatment plant for final disposition, it was necessary to convey the sewage from the district to the city's Seven Mile road sewer. This connecting sewer in Andover avenue was necessary to enable Oakland county and the city of Detroit to perform and carry out their contracts relative to sewage transmission and disposal.