Maybe use an Al 40 next timeThis is the way to go. Razor blade. Seal around a 2l bottle. Do the complete cut in one go, if possible.
If it's a 2l bottle, it needs to be full/sealed, so it doesn't push in while you do it.
But, be very careful, because a suitably sharp razor blade will also easily puncture a plastic 2l bottle and spray soda everywhere. Ask me how I know. Okay. Don't ask. You already know.
