The present disclosure is directed to a valve structure that comprises a flexible structure having a distal portion configured for attachment to a first member and a proximal portion configured for attachment to a second member. The flexible structure is configured such that when the first member is extended distally relative to the second member, the flexible structure adopts a reduced width profile and such that when the first member is retracted proximally relative to the second member to a point of maximal retraction, the flexible structure adopts an expanded width profile, which is more resistant to deformation due to fluid pressure in a proximal direction than it is to deformation due to fluid pressure in a distal direction. The present disclosure is also directed to devices and methods pertaining to such a valve structure.