A method of mechanical twist lock attachment of a pass-through valve or fitting over an aperture in a plastic fuel tank having an embedded vapor barrier layer. A ring having circumferentially spaced internal lugs is secured to the tank by weldment around an aperture in the tank wall exposing an edge of the barrier layer. A seal ring on the pass-through is located in the aperture to seal the exposed vapor barrier edge. Outwardly extending projections on the pass-through attach the pass-through by twist locking engagement with the projections on the ring.