In piping engineering terminology, a "reducing tee" specifically refers to a T-shaped connector with three interfaces of different nominal outer diameters. Two of these are straight-through outlets of the same diameter, and one is a vertical branch outlet. The diameters of each of the three outlets must be different from the main pipe outlet, or at least one outlet must differ from the main pipe outlet. The national standard GB/T 18742.3 explicitly requires that the markings be written in the order of "main pipe inlet × main pipe outlet × branch pipe outlet," for example, "32×25×20" indicates that the main pipe is reduced from 32mm to 25mm, and the branch pipe has a 20mm diameter. This structure naturally adapts to the piping logic of a household hot and cold water system, where the main pipe is thicker and the branch pipe is thinner, avoiding water resistance and noise caused by sudden expansion and contraction.
When renovating a bathroom, the original wall-embedded main water supply pipe was 32mm, but the shower hose and angle valve interface are 20mm. Forcing a connection in the middle easily leads to leaks and bulges. I tried a combination of a regular equal-diameter tee and reducers, but it required two heat fusions, the angle was difficult to control, and each additional seam increased the risk of leaks. Later, I used a reducing tee with three selectable sizes: 20/25/32mm. One heat fusion was all it took to reduce the main pipe diameter and allow for side extension. The pipe walls are thick, the weld joint is neat, and it inserts firmly without wobbling. After melting and cooling for five minutes, it can be pressure tested. The surface is matte and smooth, without burrs or scratches. It stacks neatly without taking up much toolbox space. The dimensions are clearly printed, so there's no need to consult manuals or tables; you can easily pick one up and know which section of pipe it corresponds to. It's convenient to use with PPR pipes, like a hidden "brain" for your water supply system.
