So are you making bubble hash (cold water mix, strain, separate, strain, etc) or pressing kief (kief from 4 pc grinder or kief box)? Ask because storage can be a bit different. If making bubble, you want to be sure it is TOTALLY dry before storing, because it can mold if not fully cured. If pressed kief, this usually isn't a concern.
Agree well sealed mason jar (smaller the better) is best. Best for either, but again you want to make sure bubble hash has dried out first.
I have a vacuum pump that I use for long term storage that works extremely well for hash. You can use any mason jar or any old jar that still has its rubber seal intact (like a jelly jar). What you do is poke a hole in the lid with a super thumbtack (comes with it), then put this little band aid looking thing over the hole (comes with a bunch of these). Then you pump out the air. I use those tiny jelly jars for hash (like the ones in those Christmas cheese gift boxes than grandma used to send). They are only 1/2 fl oz I think, so super small. A little tricky with the vacuum rig because of size, but not too bad with just a little practice. And, OK to use a bit of a larger jar because you suck out most of the oxygen. And, creates a nice vacuum while sealing the jar. I try to be sure not to vacuum too much with fresh buds (for fear it will burst resin heads), but don't think this is an issue at all with hash/pressed kief.
The pump is called a Pump-n-Seal. I got mine years ago on Amazon for less than $25, but don't think they have them anymore. Can still get it from
manufacturer's website here for about $35 (+ S&H, I think). Not the cheapest, but has been a worthwhile investment for me. If something ever happens to mine, I'll be getting another immediately! Not only is it good for hash, but for vacuum sealing anything including any vape-ables and even food - if you can imagine that!