Abstract: This invention relates to a telescope tap to be used for the tapping of liquid from a bag-in-box where a bag containing the liquid and equipped with a spout is placed inside a box. The telescope tap comprises a base member which engages with the spout and with the box wall, a telescope pipe placed sliding extractable in the base member, a handle to extract the telescope pipe from inside the box, a knob for opening and closing the outlet in the telescope pipe, and a gap around a part of the telescope tap for slidably receiving the box wall when sliding the telescope tap into the box. The invention furthermore concerns a method of filling a bag-in-box with a fluid, where a bag with a spout is filled with a fluid, a telescope tap is placed in the spout thereby closing the bag, a cut is made in the box, and the bag then is slid into the box with the tap fitting the cut in the box.