I've got a persisting problem I could use some help with, if anyone has
experience.

I tend to buy flour in bulk in large paper sacks that would ideally last
me about a year or so, if not more. The problem is that, inevitably and
usually in the summer, moths manage to crawl inside at which point the
whole batch is pretty much unrecoverable. Trying to seal the sack has,
at best, only delayed the inevitable, so I'm wondering, does anyone have
any advice on how to deal with this?