<p>Dumbledore states that potion's aim is not to kill but weaken the person until voldemort arrived. But this has been proved wrong since no alarm system alarmed voldemort when both real and fake locket taken. It is believed that potion weakens person in order to kill the thief in a torturous way but it has seemed to me as a mistake. But it is clear that potion dont kill the drinker. And Regulus chose to die there (not because of potion because of inferis) since he believed that he cant go on and fight voldemort. You can find these in this page. in the behind the scenes section.</p><p>And i think basin refills itself too. I think voldemort didnt refill it for one go when he refilled. It was a permanent refilling charm or something because after dumbledore dinks it and voldemort go back there before battle of hogwarts to check and find basin full with potion then make it clear like water and see nothing in it. Since dumbledore didnt refill it when he leaves its a self refilling.</p>