Method for molding and sealing hollow plastic tank

A method for manufacturing a hollow parison includes forming a parison (10) having a wall (12) of multiple layers of polymer including a barrier layer (38), and open ends (14,16), each end having an end surface extending around the periphery of the respective end. A mold (20) is formed having a first section (22) and a second section (24) facing the first section (22), the mold forming a cavity between the two mold sections (22,24) when the mold (20) is closed, and defining surfaces to which the parison conforms when the mold (20) is closed. The mold sections are closed on the parison (10) such that in the mold (20) at each end of the parison a first portion of each end surface is compressed against a second portion of the respective end surface. The mold sections (22,24) are further closed on the parison such the barrier layer (38) of the first portion and second portion of the end surface at each parison end are joined and welded mutually along a seal line. Then the mold (20) is opened and a hollow, formed tank is removed from the mold (20).