Buckets with the lids with the rubber o-ring, like paint buckets and most others, will also keep things like concrete mix, grout and mortar mix from hardening, like they will even in an unopened bag. A lot easier to scoop something out of a bucket than a bag without making a mess. Dump it in and get rid of the bag. Also, it’s a good idea not to store stuff right on your floor, an exception being stuff in plastic buckets. Don’t know about everyone else, but most of my buckets are from dumpsters. You just have to let any remaining paint dry and can easily peel it out. Washing’s not necessary.