Decide what size of filter pores you need. From online lab supply stores, you can order filters with pores as small as 0.1 micron.
Determine whether filters need to avoid protein binding, allowing proteins to pass through into the filtered solution. If so, consider purchasing filters made up of material such as polyvinylidene difluoride (PVDF) or polyethersulfone.
Determine which chemicals are present in your sample that are potentially caustic. Accordingly, pick a filter that does not interact with these chemicals.
Set up your filter and sample for filtration. If you need to sterile-filter your sample and avoid exposure to the outside air, filter it in a tissue culture hood, which is a standard piece of lab equipment, typically used to culture cells. A tissue culture hood is equipped with a glass veil blocking most outside air from entering, and a fan to continually circulate air in the hood, to maximize the purity of the air inside the hood. Leave the filter in its original plastic packaging and spray it with ethanol before placing it in the tissue culture hood. Open the filter and attach it, with vacuum tubing, to the vacuum filtration apparatus in the hood. Pour wastewater into the top of the filter, replace the lid on top of the filter, and turn the vacuum filtration apparatus knob to create a vacuum in the vacuum filtration tubing, subsequently causing the liquid to pass through the filter pores. Depending on the size of pores, this could take between minutes and an hour.
Conduct step 4, if you do not need to sterile-filter your sample, at a vacuum filtration apparatus outside the tissue culture hood.
Separate the bottom part of your vacuum filter, containing your filtered sample, from the top part. Cap and save the sample. Discard the rest of the filter.