Make a drilling jig by cutting a square piece of 2x4, which would be 3.5 inches on each side. On each face, draw a line that bisects each opposite corner, which will produce a perfectly centered X. Then, on each edge, find the midpoint and drill perpendicularly toward the center of the block, this will leave two holes at right angles that bisect at the midpoint of the X’s on each face. With a hole saw the diameter of the pvc pipe, drill out the middle of the block using the X’s on the faces to locate the precise center of the square. Then you can slip the pvc through the block and use the perpendicular holes drilled on the edges of the block as guides to perfectly align and drill the four holes on the pipe and keep them at perfect right angles to each other. Drilling out the jig with a drill press would be the most precise, but even just eyeballing with a hand drill will be better than trying to eyeball and drill the pipe freehand.