To distribute crushed Oyster shells I have a 3" pipe end-cap with a drainage hole zip-tied to the wire. So far with my three Runner girls it lasted about a month, but during the last couple of days my new ducks have discovered their need for extra Calcium and i must fill it up every 2-3 days. Each of the two drakes tried it once, figured out it wasn't tasty and they ignore it since then. I don't feed any "layer" feed, only "meat-bird" crumbles/pellets.