A connection assembly configured to deliver a medical liquid to a container is described. The connection assembly includes a connecting member connected to the container, an attachment member, and a sealing element. The attachment member defines a lumen, a first end to be connected to a delivery device, and a second end connected to the connecting member. The sealing element is disposed in the lumen of the attachment member and includes a sealing head, a flange, and a foot portion. The sealing head seals the lumen of the attachment member, and the flange and the foot portion engage the connecting member.