to expect a screw-top lid to keep the liquid inside even when the bottle is lying down?

[EasilyDistracted77]

First it was the screw-cap wine bottle, the it was the screw-cap milk bottle leaking all over the fridge. And the point of the lid is .... what, exactly?!

It's to keep things fresh/sealed so to avoid things getting contaminated. Never lay them down once open.

Nope. I think it's high time milk bottles and cartons with screw top lids did the job they are expected to do. If other bottles with screw tops don't leak (like coke, beers etc) then why should the milk?

...and if milk can come out, then germs can get in.

Ah, milk lids aren't proper screw tops. The clue is in the fact you have to pull that little foil seal off when you first remove the lid. If they were watertight there would be no need.

I would imagine that an opened-then-closed wine bottle would seal properly, but an opened-then-closed plastic milk bottle would not.

And what Mackerel said about the foil seal.

I know this to my expense, when I transported my dog's urine sample to the vets in a plastic milk bottle within my handbag.

MackerelOfFact No, those little foil stuck on circles are there so that no one can take the screw top lid off and put something noxious into the milk. The same can be found with that plastic 'bracelet' around the lids of jars of jam or the plastic tubs of dips or coleslaw. They are there to stop people contaminating the contents.

If they are not there, a prospective buyer will know that they have been tampered with.

I'd like it if the drinks bottles that you put in the DC lunch boxes, were also leak proof. Manufacturers must know that kids bags end up upside down at some point in the day.

Llanarth Nice.
How on earth did you manage to get a urine sample from your dog - I'm very intrigued! I remember once trying to get a urine sample from my little boy when he was under a year old, and that was NOT easy!