My Newsouth Boost gauge turned up today courtesy of Wazzzer, this might sound like a bit of a daft question but I'm going to ask it anyway

I've bypassed my n249 valve so I've got tubing going from the FPR straight to the top of the DV, shown in blue here (it is now red though!)

I was going to T into the tubing close to the FPR, the tubing has an
ID of 3mm. The problem being that the tubing on the back of the boost gauge has an
OD of 3mm. I have a 3mm T-connector, but obviously that will not connect all the tubing together.
My question - do I need to get a reducing T-connector? If so where from? Or do I connect the 2 different sizes of tubing with a reducer and use my existing T-connector?