The optional plumbing kits include fittings and hoses to make the fuel pump hanger a direct bolt-in OEM replacement for both single and dual pump configurations. These kits do NOT require any extra fuel hose plumbing excluding Subaru FA20F engine applications which require an external fuel pressure regulator and corresponding hoses. The single pump plumbing kits include plug n' play adapter fittings for the fuel pump outlet, FPR return inlet, and crossover hose underneath the rear seats. It reuses the OEM hard lines.