Hi.

I need to connect a 15mm cold water overflow pipe to a 40mm 'Tee' waste system.

Any idea on how I go about doing this?

Thanks.

I'm a Florida plumber so I had to convert metric down to our pipe size. As I understand the question you wish to take off a 1/2" ID. branch from a 1 1/2" ID. Main. You will need a 1 1/2" X 1 1/2"X 1/2", (40 mmX40mmX 15 mm) drainage tee to do this. If you can't get a tee with a 1/2" branch, get the one with the smallest branch and bush it down. If you're asking how to install it I would have to know the type of pipe, (PVC,Cast iron, Copper?) and how tight a space you're working in. Good luck. Tom