As the title states, does anyone know exactly what size (ID) of hose I need to replace the drain lines? I'm talking about the rubber hoses, and not the metal drain tube coming off the turbo. Thanks!

 

For what it's worth, I dug up the greddy manual and it looks like the hoses are 15mm, which corresponds roughly to 5/8 or -10AN. It also uses the same hoses for power steering return, so whatever the OEM power steering line size should work too.