Keep Sawdust From Clogging A Shop-Vac's Filter With A DIY Pre-Separator Patrick Allan Feb 11, 2016, 5:00pm 0 Video: The more you use your Shop-Vac, the more suction you lose as its filter gets clogged up. This DIY pre-separator will help prevent your Shop-Vac's filter from clogging, and keep its suction power from deteriorating.