Gray water question

[moby]

...and mine have had their best year so far! Started the season with two that I managed to over wintered successfully again in my G/h, now there's over 2 dozen of the things bobbing around in the pond. Whilst they're not huge, im now wondering what size bendy bucket I need to buy to get them safely through this coming winter? I used the 1pint lidded plastic tumblers they were sold in for previous winters, but I haven't got 24 of those!