I followed a tutorial from HERE
, ignoring the part about the reeds. This will yield a 100% duct tape bagpipe bag.
As a side note - I used 1/2" OD vinyl tubing for my bag stocks on my first iteration, but I highly advise using 1/2" CPVC instead. The vinyl compresses when you try to put the drones and chanter on, and are kind of slippery compared to a snug CPVC fitting.
I started off by making a big flat sheet of duct tape - lay one strip down sticky side up, then place one halfway up sticky side down. Flip and repeat until you get something roughly 23" square.
Then fold the sheet over halfway, draw your bag outline, and cut it. Try to get the seams to match up as seamlessly (heh) as possible. For mine, I drew a straight line for the bottom of the bag about 12" long and a chanter neck about 4" long and 2" high, then eyeballed the rest and joined them with a curve.
Cut your stock pieces (roughly 2-2.5" apiece) and line them up with where you want them to go. On my new bag, I have three on top spaced roughly 1.5" apart. The blowpipe goes in front, then the tenor drone, then the bass drone, but really you can place them anywhere that's comfortable for you.
Next, insert your stock pieces. DO THIS BEFORE YOU SEAL THE BAG. It may seem obvious, but it's easy to forget, trust me. The stock pieces can be secured with duct tape again, but make sure you have a tight seam especially inside the bag because it's quite the pain to re-seal them if there's a leak.
Finally, close up your bag by taping lightly around the seam. I guarantee you there will be air leaks, so blow into the bag, find a leak, duct tape, and repeat. You do this without the drones on by putting some tape over each stock hole while you test it.
During play the bag will also start to leak initially. Just stop playing, grab your duct tape, and get fixin'.