A sampling port (10) has a generally cylindrical first portion (36), a generally cylindrical second portion (34) with a smaller diameter than the first portion (36) and a guide member (66) that rotates about a hinge (56) to extend into the second portion (34) to reduce the effective diameter of the second portion (34). The guide member (66) and/or the second and/or first portions (34, 36) are shaped so that the guide member can extend further into the sampling port (10) than a simple cylindrical guide member rotating into simple cylindrical first and second portions.
