Like already said Al foil is a bad idea.

And Lye (NaOH) is not "more toxic" than pickling lime (Ca(OH)2). Both chemicals are definetly not something you should eat but they also wont kill you if ingest some. Both chemicals are used extensively in food processing and they both can be bought in food grade quality, possibly even in medical quality.

The danger comes from the fact they are caustic. They are NOT toxic. Especially concentrated and/or hot solutions will damage skin. But thats mostly only the outer layer and if you wash it off quickly you wont even damage your skin. (Hence the reason why when im in the university lab no one wears gloves except in rare cases. Common fallacy for people to wear gloves when the gloves do more harm than good)

Also NaOH does NOT attack plastics. That comes exclusively from the NPS like naptha or whatever you use.
NaOH does attack glass but thats not really something that happends in aqueous solutions. You do need to have a fully concentrated solution that is boiling hot to even attempt to deal visible damage to glass. Also borosilicate is dissolved by NaOH as well. Borosilicate glass doesnt have a much higher chemical resitance but it has waaay more heat and temperature shock resistant.

For use as a bottle I recommend any glass bottle really. For a cap I recommend any cap and just buy a PTFE sheet and make an insert. This will hold up to nps and NaOH forever.

That's a really interesting idea. Can you elaborate a bit on how you would do the insert. I am not sure I really understand; Like how does the screw cap still fit in with this insert?

Would something like this work? Or is it not enough when it is 'PTFE coated'? https://www.esska.se/sho...;hc_fcv=XpNJ9BCHAtReutb0~LdB8x4w27f9vhkIAzzzzzzzz~LdB8x3k27f9vgkI9zzzzzzzz