The two most common ways to filter a solid at microscale are as follows:
With the aid of a Pasteur pipette
If you want to remove the supernatant liquid from a solid in a vessel (vial, Erlenmeyer, etc.) you can use a Pasteur pipette.
The pipette, provided with a teat, is introduced to the bottom of the container, so that it is completely stuck to the container, and it is sucked so that the solid will remain at the bottom and the liquid in the pipette.
If the solid is made up of very small particles, we can use a cotton ball wrapped around the tip of the pipette to prevent the solid from passing into the pipette.
If a solid is to be removed, a pipette is prepared with a small amount of absorbent cotton, which is introduced into the pipette with the aid of an applicator, for example a piece of wire.
Next, a filling material, such as cellite or silica gel, is introduced and then the pipette is fixed to a holder with the aid of a clamp.
The liquid to be filtered is transferred with the aid of another pipette fitted with a teat and the filtrate is collected in a container. The solid to be removed will be retained in the filling.
If the passage of the liquid through the filter is very slow, a plastic syringe can be attached to the filter by means of a piece of rubber tube and force the dripping by generating a pressure through the syringe.
By means of a Hirsch funnel
A Hirsch funnel, either glass or plastic, is used, similar in shape to conventional vacuum filtration, assembled to a Kitasato or a tube with a side outlet to connect to the vacuum.