No member of the council shall be appointed city manager nor shall any member hold any paid municipal office or employment under the city; and until one year after the expiration of his term as mayor or councilman no former member shall be appointed to any paid office or employment under the city, which office or employment was created or the emoluments of which were increased during his term as councilman, and no mayor or councilman shall hold any other office which is incompatible with such offices under the laws of the State of Minnesota. Nothing in this charter shall, however, prevent a paid volunteer fireman from serving as mayor or councilman.