Sadistic? ...In any case, it doesn't make much sense. If Jill has a method for which she can test for poison without drinking it, why is there a taste tester? If Jack is going to drink it regardless, then why test for it?

Let's put it this way. If Jack drank from the pail, then he was only doing his job. Perhaps he noticed it was poisoned, which is why they did not bring the pail back. What follows is an unrelated sequence of events.