I've never used a foam filter as a primary (not that there is anything wrong with doing that I don't guess. ). I've used them as pre-filters on ATV's and mowers. My process was usually to clean the filter with TSP, then pour 30wt oil on it inside of a zip lock bag. Squeeze the bag real good to saturate the filter, then remove it from the bag. Next step was to wrap the filter in a pile of paper towels, and squish it pretty good. Soaking up the majority of the execss oil. It will still get dirt caked up all over it. Try the TSP for cleaning. About a teaspoon/gallon of water.