[0109] To guide the pipette tip 71

[0109] To guide the pipette tip 71 to a through-hole 23 in the lid housing 8 and the middle of the apertures 15, 6 in the first and second resilient layers 13, 4, the pipette tip 71 is guided by the guide elements 2 of the guide structure 1. The guide elements 2 act like funnels for guiding the pipette tip 71 to the through-holes 23 and the middle of the apertures 15, 6 and keeping the pipette tip 71 centered in this location during agitation of the container assembly 200. After the pipette tip 71 is removed from the apertures 15, 6, the apertures close by themselves through the elastic nature of the first and second resilient layers 13, 4.