down is an add for "Savage Marine silencers" which is the construction technique used in my old system. A pipe within a pipe. The flange at the manifold was connected to the inner pipe. About 4 inches away the outer pipe started and followed the the same bends as the inner. When it reached a bend that they couldn't match both the outer and inner pipes stopped, two new flanges were added and the outer pipes were joined by a rubber connecting hose to jumper the water. My system had three different parts. The final section injected the water into the exhaust port at the stern. It was essentially one long pipe from the engine to the transom with an outer sheath which contained the exhaust water to cool the inner pipe. The dang thing was all thick wall bronze pipe, weighed a ton and sounded like a, well, like a tractor with a straight pipe exhaust.:-)