[Closed] Whisky afficianados - what flask?

What's the ideal flask for whisky taste preservation? I've got a stainless flask and I had no problems with it for a couple years, regularly finished the contents, rinsed, refilled. Every now and then it's sat half full for a month or two. Last time out, the dregs were pretty grim. cloudy, with bits in. Looked a bit like rust.

What next?

I'm guessing something glass lined would be ideal. But I'd have thought stainless would be pretty good. Presumably "stainless" could be any grade. Can you get surgical steel flasks? What else? There are Ti flasks, but somehow I think that would affect the taste more.

Any thoughts? Be nice if it was hip flask shaped, as I've got one of those flask cage jobs for the bike.

Ta!