Is this the filter you use? https://www.medical-and-lab-supplies.com/filtration/disposable-vacuum-filters/500ml-millipore-steritop-btf-durapore-pvdf-membrane.html?___SID=U
How long does it take you to filter 500ml?
I tried using the Whatman Zap-cap 0.2um filter with nylon membrane that a lot of people recommend using and even with enough vac pressure from an electric vac pump, it dripped very, very slowly to the point I gave up because it would have literally taken all day to filter 500ml. I was using GSO which does not have a high viscosity. I think the reason it filtered so slowly must have been because the membrane was made from nylon, but I could be wrong.