GST on retained feedstock: refinery liable on net quantity retained; returned volumes taxable when resupplied elsewhere. Where LPG and Polybutylene feedstock are supplied by a refinery through dedicated pipelines and manufacturers retain only part of the supply for manufacture of specified products, GST is payable by the refinery on the net quantity retained by the manufacturer; the refinery must account for GST on the returned quantity when it later supplies that quantity to any other person. This clarification is limited to GST law.