I don't have the silencer. The drawing was the plan i'm sure but mine just has the high backwash loop.
My flange does have some rust, yes, but it's It's the jacketed part that is just shiny metal with some thin copper-colored paint that flakes off easily. I would think that galvanized pipe would be a dull zinc color and all corroded. The pic shows the single-wall pipe from the manifold flange—still all nice. That gray is spray galvanizing. Don't bother.
Photo also shows where the paint is flaking off from some kind of reaction to the green copper oxide from the bronze ell at the water inlet
I keep forgetting to confirm what type of metal it is when I'm at the boat. Sorry.
Anyway maybe if Jesse's is the same, he can check his alloy type.
Russ