Not sure if this is exactly what you're going for, but if you have a run of pipe and you want to 'T', sketch a line perpendicular to the existing line and then drop a flange or other fitting that you want coming from the 'T'.
Then, right click on the point from the line you sketched perpendicular to the existing line that is coincident with your original line and select "Penetrate".
It'll act as if you cut a hole in the first pipe and then welded the 'T' into it as another pipe.