Cap and tube set for use in a medical procedure

A cap for a container having an annular open neck, the cap comprising an annular collar with a longitudinal axis and a diameter perpendicular thereto, a side wall with open upper and lower ends and an annular flange projecting inwardly from the side wall at the upper end, and a seal comprising two seal elements which co-operate to form a generally cylindrical seal member, the seal elements each provided by a block of elastomeric material shaped and dimensioned to fit side by side within the annular collar to form a tight fit and to contact and seal against each other and against inner surfaces of the collar with no gaps to provide the cap which can be fitted onto the open neck of the container, with the seal elements in contact with each other in a plane parallel to the longitudinal axis and an upper surface of each seal element is exposed in the upper open end of the collar, and wherein at least one seal element comprises at least one opening therethrough.