A method for manufacturing a manifold assembly (220; 320) with internal fluid communication between a first manifold defining a first fluid chamber and a second manifold defining a second fluid chamber of said manifold assembly, the first manifold and the second manifold joined in parallel relationship along a longitudinally extending interface between a wall of the first manifold and a wall of the second manifold, said method comprising: forming a first access port (226; 326) in a wall of one of the first manifold and the second manifold diametrically opposite the interface; forming a first fluid communication port (230; 322) extending through a wall of the first manifold and a wall of the second manifold at the interface, said first fluid communication port defining a first fluid passage between the first and second fluid chambers; and sealingly plugging the access port; wherein each of the first and second manifolds has an internal diameter; and characterized in that the method further comprises at least one of: sizing a diameter of the first fluid communication port such that a ratio of the manifold internal diameter to the communication port diameter has a value in the range from 3 to 13 for each of the first and the second manifolds; and selecting a longitudinal spacing between adjacent communication ports connecting the first and second manifolds such that the ratio of communication port spacing to the manifold internal diameter has a value in the range from 0.5 to 4 for each of the first and second manifolds. forming a first access port (226; 326) in a wall of one of the first manifold and the second manifold diametrically opposite the interface; forming a first fluid communication port (230; 322) extending through a wall of the first manifold and a wall of the second manifold at the interface, said first fluid communication port defining a first fluid passage between the first and second fluid chambers; and sealingly plugging the access port; wherein each of the first and second manifolds has an internal diameter; and characterized in that the method further comprises at least one of: sizing a diameter of the first fluid communication port such that a ratio of the manifold internal diameter to the communication port diameter has a value in the range from 3 to 13 for each of the first and the second manifolds; and selecting a longitudinal spacing between adjacent communication ports connecting the first and second manifolds such that the ratio of communication port spacing to the manifold internal diameter has a value in the range from 0.5 to 4 for each of the first and second manifolds. wherein each of the first and second manifolds has an internal diameter; and characterized in that the method further comprises at least one of: sizing a diameter of the first fluid communication port such that a ratio of the manifold internal diameter to the communication port diameter has a value in the range from 3 to 13 for each of the first and the second manifolds; and selecting a longitudinal spacing between adjacent communication ports connecting the first and second manifolds such that the ratio of communication port spacing to the manifold internal diameter has a value in the range from 0.5 to 4 for each of the first and second manifolds. sizing a diameter of the first fluid communication port such that a ratio of the manifold internal diameter to the communication port diameter has a value in the range from 3 to 13 for each of the first and the second manifolds; and selecting a longitudinal spacing between adjacent communication ports connecting the first and second manifolds such that the ratio of communication port spacing to the manifold internal diameter has a value in the range from 0.5 to 4 for each of the first and second manifolds.