Abstract: A method of making a tank includes the steps of forming a pair of top and bottom half members by deep drawing, welding at least one tank connector assembly in an opening in one of the half members and fastening the top and bottom half members together by welding to form an outer shell having an internal surface. The outer shell is changed with non-corrosive polymer material before or after the welding step. The tank is subjected to a rotational movement in the presence of heat to thus cause the polymer material to be uniformly distributed over the internal surface of the outer shell to thereby form an inner shell of non-corrosive material inside the outer shell wherein the inner shell provides a substantially leak-tight liner for the outer shell to thus prevent contact between the contents of the tank and the outer shell, said outer shell serving as a mold for the inner shell wherein the mold becomes a permanent part of the completed tank.