The invention relates to the filtering of liquid samples, preferably in a laboratory environment, for example for collecting micro organisms from the liquid sample for subsequent testing. The invention provides a method for filtering a liquid sample which comprises providing a blank of a deformable sheet material and a filtration medium, deforming the blank to form a funnel extending above and about the filtration medium, introducing the liquid sample to be filtered into the so formed funnel, and filtering the liquid sample from the funnel through the filtration medium, for example to a downstream receptacle. The method is accordingly based on the concept that the funnel is not or at least not completely preformed but provided in a form of a blank of a deformable material sheet which is deformed so as to form the funnel at the point and time of use during filtration.