Tub sizes for garter snakes?

Hi, I was just wondering, what size of tubs would you use for an adult garter snake? I know that there are many variates and species, but what's the biggest and smallest size you would use for an adult garter?

Also, how is the market for garters? I've seen pictures of San Francisco Garter snakes and they're absolutely stunning.

I have no experience with garters, but I would say that a sweater box (28 qt, 24 by 18) would be perfect, it has the same floor space as a 20 long fishtank. I think that bhb keeps them in those tubs.