The disclosure provides a connector for connecting to an end of a tube. The connector may include a hollow connector body having an opening for receiving the end of the tube. The connector may further include a gripping mechanism for gripping the tube to hold it against retraction and a sealing mechanism for forming a seal between the tube and the connector body. The connector body may be formed from an opaque material and include a window therein. The window may be formed from a transparent material through which an end of the tube can be seen when the tube is correctly located within the connector.