I used to install pneumatic grain conveyors using 4,5 and 6" mill pipe. If we need a flexible joint, we would use Goodyear sandblasting hose w/4pc galvanized clamps made for that purpose. It is thick, tough and stiff and seems well suited for GW's intake pipe extension.
GW the Ys were just a thought I had that would allow easy access in case of a plug.
As far as the traps go, look under your kitchen sink. There should be a trap there as with all other connections to wastewaster pipes. The idea behind it is to keep the sewer gas from exchanging with the air in your house (so your house doesn't stink) while still allowing water to flow freely. It's purpose is not to "trap" lost jewelry. The same principal applies to your siphon systems. The trap helps keep air from entering the system at the discharge.
