Members of the board of directors of an operating agency shall be paid the sum of fifty dollars per day as compensation for each day or major part thereof devoted to the business of the operating agency, together with their traveling and other necessary expenses. Such member may, regardless of any charter or other provision to the contrary, be an officer or employee holding another public position and, if he or she be such other public officer or employee, he or she shall be paid by the operating agency such amount as will, together with the compensation for such other public position equal the sum of fifty dollars per day. The common law doctrine of incompatibility of offices is hereby voided as it applies to persons sitting on the board of directors or the executive board of an operating agency and holding an elective or appointive position on a public utility district commission or municipal legislative authority or being an employee of a public utility district or municipality.