Hi Linda,
Sorry for the delayed response. It's been a whirlwind of activity for me: painting and creating my studio/playroom, helping my son move in this blasted heat, and enjoying a quick trip to see family in Colorado.
As far as the PVC drip system we have, my husband came up with the idea. I had to look up Mittleider and, yes, it does seem to be fairly the same. Basically, we tired of using soaker hoses. They would spring a leak, are too heavy to move, and, well, we just weren't fond of it for our age group. So, Phil took measurements and created a three section PVC pipe grid that met our raised horseshoe bed. Each section has rows and is hooked up to it own valve on our four-way. We leave the fourth valve to use for our garden hose to water outside the raised bed.
After gluing the PVC sections together, we simply placed it on our deck and drilled 3/16" holes every six inches (on one side) along the rows. There is nothing else. The pipes fill with water and drip out of the holes. Afterwards, we used wooden blocks to raise the PVC above ground level (holes faced down) in the bed. When it's time to plant, I plant along the plastic rows knowing water is along the area.
It has worked out beautifully for us. We can water by zone as each section has it own valve, we can water the entire bed at once, and, because of the additional section Phil added later, it now waters the plum trees outside, but nearby, the main bed. The only manual effort is to remove a PVC riser which opens the system. No more dragging the garden hose around!! Plus, it can't act as a clean out, if needed.
When it's time to pull plants and/or turn soil, the PVC sections are disconnected from the garden hose leaders which connects them to the valve station. Although, they are lightweight, it takes the both of us due to their floppiness, the perimeter fencing to keep rabbits out, and their sheer size (8x25?).
I hope that explains our system. I'm not sure I answered your question about holes being straight, though. Phil looked into making an adapter to drill into the round pipe, but when it got down to it, applying a little pressure to the pipe with a foot, or knee, kept the pipe steady to drill the holes. We did use a yardstick to get the 6" hole spacing, but someone with a good eye won't even need that. I think the key was to pre-assemble, and glue, before drilling the holes.
Happy Gardening!