Homemade filter paper
Apparently, the particles of your solid are either very small, or / and not crystalline.  This may complicate filtration, though this is one of the reasons filter papers used in the chem labs are sold in different grades of paper hardness.
A practical alternative to separate such a slurry from the liquid phase would be to substitute filter and funnel by a centrifuge.  With some luck you still find some with a manual crank (with conic tubes, about $\pu{20 mL}$ each). Based on own experience, this often is faster than setting up and then performing a suction filtration over a glass filter. On small scale, it is simpler to wash the slurry, and clean up the tools, too. Just keep the opposite tubes balanced and don't mind the surprised gaze of your colleagues around.

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