In certain embodiments, a vial adaptor for removing liquid contents from a vial comprises a piercing member and a bag. The bag can be contained within the piercing member such that the bag is introduced to the vial when the vial adaptor is coupled with the vial. In some embodiments, the bag expands within the vial as liquid is removed from the vial via the adaptor, thereby regulating pressure within the vial. In other embodiments, a vial comprises a bag for regulating pressure within the vial as liquid is removed therefrom. In some embodiments, a vial adaptor is coupled with the vial in order to remove the liquid. In some embodiments, as the liquid is removed from the vial via the adaptor, the bag expands within the vial, and in other embodiments, the bag contracts within the vial.