Depends on how often you need Rats. If you are simply breeding for pets and can just keep them around as they grow until they sell, then you can just keep them 1:3 at all times. Personally, having 16 snakes, I need all sizes of rats every week. I stagged 2 males through 8 tubs (although for you it would be 1 through 3-5 tubs) that way I always have a new litter coming.