The last time I used a non spec plastic bottle was a two nighter, and was trying to keep volume low. Used a small bottle with only 100ml in it, all I needed and it was so small I could easily fit it into a small space in my half frame bag. Turn. C
Before that I'd use the same container on a different over nighter, and used the empty coke bottle when I had to buy some alcohol from some lady's house in some small town somewhere in Latin America.
Didn't leak!