How do I intersect two hollow cylinders at 90 degrees to each other to form a TEE? I extruded them from the sketch, but when I insert a boolean operation, split, it tells me
You might find it better to model two solid tubes in one partbody and then use the shell command. This would also help if you had to come back and edit the model later.
I liked SolidKat's method better, but I tried it as Descatia described, using a UNION TRIM operation. I got a similar message if I tried to select the Part Body first. But it worked OK when I selected the Body first and the PartBody second. see attachment