Blender Pipe Joints
Pipe Joints - I've rendered here all of the default pipe joints (white) under Blender 2.8's "Mechanical - Pipe Joints". I made the copper ones from the white ones. Although the 5 types are Pipe Elbow, T-Joint, Y Joint, Cross-Joint and N-Joint, you also can make custom ones with more openings and different angles when you first add them. Choosing smooth shading on these can have undesirable effects if you are rendering them, so I'd recommend increasing the number of divisions from the default 32 to something higher (here they are at set to 64 divisions, but increasing them to 128 would make them look even smoother, but for those who care about render times in an animation project this would increase the number of mesh vertices in a large project substantially.)
Kohler has a website where you can get thousands of 3D bathroom and plumbing fixture models in including .obj format.