An adapter having a female coupling configured to receive and establish a friction seal with a male coupling of an external device for inserting or extracting a liquid to or from a container, by applying a load to the male coupling after inserting it into the female coupling, the load being provided by the weight of a portion of the external device, the adapter being configured for insertion in a mouth of the container and secured therein using a stretchable membrane that fits snugly around the mouth of the container for obtaining a tight seal, the stretchable membrane having tabs for a user to grasp.