Hi Karen
OK, the bottles. I have some thoughts that the standard hard Nalge seal at the neck of the bottle is by now a bit old, even obsolete. It features a hard plastic to hard plastic contact, and has to be done up tight to work. But look at the lid on any food bottle these days and you will see a softer sealing ring under the lid. These hold a good vacuum and don’t leak oil (eg marinated dried tomatoes!).
I have some nylon fuel bottles made by Nalge for kero and white gas. They have the hard Nalge seal, but I was never happy about the way they always smelt of kero when I was using a kero stove. Not at all good inside a pack. So I found a nice fat O-ring size which fitted snugly inside the cap, and fitted such O-rings (nitrile) in all my fuel bottles. That softer seal worked well. (I have some of those fuel bottles still, for sale.)
I have also used the common 1.25 L PET rocket-based bottles for kero for food caches. The cap has a small diameter and has a soft sealing ring inside it. That too has worked well. Mind you, a fuel refill was HEAVY!
Bottom line: I now prefer soft sealing rings on caps against the hard Nalge seal. More reliable.
Cheers
