All liquid gas meters must be of a positive displacement type equipped with a vapor separator or provided with other equipment which will positively eliminate all air and vapor from passing through the meter with the liquid gas, and a differential pressure regulator. The meters must be corrected, prior to use, to sixty degrees Fahrenheit [15.5 degrees Celsius] liquid gas temperature and all deliveries of liquid gas through such meters must, at the time and place of delivery, be temperature-corrected to sixty degrees Fahrenheit [15.5 degrees Celsius] and the customer billed accordingly. It is unlawful to make retail sales to customers except where delivered through a fuel dispenser from any bulk delivery vehicle unless such bulk delivery vehicle is equipped with and dispenses said liquid petroleum gas through a liquid meter as herein provided. Liquid meters may not be equipped with a bypass around the liquid meter. The prohibition of a bypass does not prohibit the use of an equalization line.