Have already caught some rats in the attic with spring traps, but want to make sure I get them all. Is there a poison that will cause them to become dehydrated, resulting in their leaving to look for water and dying outside? Online research leads me to believe that such a poison might be a myth. I'm sure that posions would be effective, but I don't want dead rats in the attic stinking. Does anybody know definitely?

By the way, I think I know where they're getting in and will eventually seal it up, but not yet if there's a chance of making them leave by the same way.