Except as provided in Section 25163, it is unlawful for any person to clean septic tanks, chemical toilets, cesspools or sewage seepage pits or to dispose or aid in the disposal of the cleanings thereof, for any person or firm engaged in the business of cleaning out septic tanks, chemical toilets, cesspools or sewage seepage pits or disposing of the cleanings thereof who does not hold an unrevoked registration as provided in this article.