One of the most popular places to buy wine this way, is at Consorzio Produttori Vini Manduria, in the Taranto province.
You may bring your own container or purchase plastic bottles. After the staff fills your bottles, you will go to the cash register to pay for your wine. Prices typically vary according to the alcohol content of the wine. There is frequently a line, so you'll have to be patient. You can shop their bottled wines while you wait; there is also a museum located in underground which has exhibits of wine history.
Italian Ventures, your Virtuoso® travel agency, in Bass Lake, Fishcamp, & Oakhurst, CA