When liquefied petroleum gas is sold or delivered in package form and the cylinder or container is connected to the consumer's apparatus, the said cylinder or container shall neither be disconnected nor removed from the premises before it becomes empty, except as may be provided hereafter or by contract with the purchaser or consumer. When removed before becoming empty said cylinder or container shall be weighed by the seller to determine the quantity of liquefied petroleum gas remaining in such cylinder or container and a written receipt issued to the purchaser or consumer stating such quantity. When weighed on the customer's premises, weight shall be subject to verification by the seller at the dealer distribution point or the filling plant to determine whether credit is due the customer; provided, however , that the provisions of this paragraph shall not apply where they are inconsistent with the terms of a written contract of sale. 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.
N.J.S. § 51:10-5