Hey Peter
I put the T-piece in the pipe that goes from the front of the turbo to the wastegate. On mine its a short black pipe kinda just next to the inlet of the turbo and goes straight down for about 10cm approx.
I needed a bigger T-piece because the one that came with my boost gauge was only for about a 2mm pipe when the pipe is about 4mm inner diameter or something so i got a brass one that me old man had lying around in the shed.
If its not being used, he don't need it
i also put clamps on both sides of the T-piece just to make sure it wont come off. again out of the old mans shed. its amazing what you can find in there
I need a longer pipe to get my boost controller on because its an L shape, not an inline one.
Cheers
Damo