When liquefied petroleum gas is sold or delivered in package form and the cylinder or container is connected to the consumer’s apparatus, such cylinder or container shall neither be disconnected nor removed from the premises before it becomes empty except as may be provided for by contract with the purchaser or consumer. Such cylinder or container shall be weighed by the seller to determine the quantity of liquefied petroleum gas being removed in such cylinder or container and a written receipt issued to the purchaser or consumer stating such quantity, which shall be subject to verification at the dealer distribution point or the filling plant to verify the amount of credit due the customer. A cylinder or container shall be considered empty when the gross weight of the cylinder or container does not exceed the tare weight as marked within the tolerance allowed.