The Board of Directors of such district is hereby authorized and empowered to make all bylaws, rules and regulations, penal or otherwise, that shall be necessary for the full protection, maintenance, management and control of a sewerage system of said district, including the lines of conveyance, plant and other property used in connection therewith and said Board of Directors shall have the power to divide such sewer district system into three (3) classes to be known as Public, District and Private sewer lines. That the public sewer system shall consist only of the main lines of conveyance to the sewage treatment or disposal plant or outside system, and the main lines for general collection, including such other property as may be necessary in connection therewith for the proper maintenance and use of such sewage system throughout such improvement district, and such public sewer lines shall be established along the principal courses for collection at such places to such extent and of such dimensions and under such regulations, as may be provided for in the bylaws or regulations or orders of said Board of Directors of said district, and such principal lines of collection may be extensions or branches of lines already constructed or entirely new throughout, as may be deemed expedient. Such public main lines and sewage disposal or treatment plant, including the other property necessary to operate such system, shall be paid for by the district as a whole. District sewer lines shall be established within the limits of all subdistricts which subdistricts shall be prescribed by the bylaws, regulations or orders of said improvement district and connected with the public sewer lines or other subdistrict lines. Such subdistricts may be again subdivided or may be enlarged or changed by a bylaw regulations or orders of the improvement district at any time previous to the construction of the district sewer line therein and more than one sewer line may be laid in a subdistrict if deemed necessary by the Board of Directors. The Board of Directors shall cause district sewers to be constructed by petition or by resolution as now provided by law for the construction of district sewers in cities and towns. Private sewer lines connecting with the public and district sewer lines may be constructed under such restrictions and regulations as the Board of Directors may prescribe by general bylaws, or regulations or orders; Provided, that the expense of constructing such lines shall be borne by the individual or individuals desiring to construct them and providing further that such improvement district shall be at no expense in the construction, repair, or operation of the same.