1 Slide the neoprene stopper over the holder outlet, if it is not already in place. Remove the funnel from
the base by turning the locking ring 1/4 turn, and rest the funnel assembly on its side on a clean
surface. Do not stand it upright, as this may soil the funnel rim or the sealing edge of the funnel outlet.
2 Seat the stopper and base firmly in the neck of the filtering flask. The filter support screen and its
underlying gasket should be in place in the top of the base, with the screen flat and flush with the base
top (see Disassembly and Cleaning for instructions on removing the screen and gasket).
3 With smooth-tip forceps, center a 47mm diameter Millipore filter on the screen (Fig. 2), with the
gridded side up if a gridded filter is being used for later statistical counting procedures.
4 If a prefilter is required to prevent filter plugging in obtaining a desired filtrate, place a 35mm diameter
Millipore depth prefilter disc exactly centered on top of the 47mm final filter. Centering must be
carefully done, so that the prefilter edge will not lie under the sealing rim of the filter holder funnel.
Fig. 2 Center filter accurately on support screen. Use forceps to avoid contamination or damage to
5 Without touching the inside of the funnel, and without disturbing the filter (or prefilter), place the funnel
on the holder base so that the nylon wheels in the locking ring are in the base slots (Fig. 3). Turn the
locking ring to the right until tight, sealing the funnel to the base.
6 If a filtering manifold is used, place an assembled holder and filter in all manifold positions, or seal off
unused positions with unperforated stoppers unless they can be closed by independent valves.