A liquid sample needle assembly is provided. The assembly includes a housing with a sample receiving chamber having translucent or transparent walls for determining whether access to the sample source in question has been obtained. The invention utilizes a highly absorbent material in a form which allows venting of gases displaced from the housing chamber by the liquid sample being obtained, which material expands upon contact with the liquid sample to provide a liquid impervious barrier. The absorbent material is in a separate sleeve-like form of a compacted tablet sleeve for rapid and easy insertion between the two hub parts forming the assembly housing. The improvement in this invention includes the use of an integral tapered post for seating the tablet to maintain it precisely concentric in the housing and on the post for causing each increment of the tablet to respond equally to an introduced sample. The arrangement herein is particularly appropriate for mass production techniques in that two housing parts may have inserted therein the separately formed tablet sleeve.