I used the Y fitting to get a better layout in the instrument panel, where T types tended to kink the tubes, before I changed to Silicon vacuum hose which is much better than the clear vinyl tube we usually use. Range of colours is good too, you can have each circuit a different colour. The Y pieces and tube came from auto suppliers on eBay(about $7 per meter). I ended up using 4mm ID as rather 5mm didn’t grip too well, no leaks but too easy to pull off. All works great now and the tubes can be unplugged easily for testing, without having to redo the ends every time.