No special filter. It's just a basic cheap wet/dry shop vac. As Binkspot said, the fluid evaporates before it even reaches the shop vac. Three 90-degree turns and a 36" vertical pipe almost guarantee it. Plus the height makes it comfortable to use while standing. Unfortunately, we had a situation that gave us the opportunity to test it out on about 80+ tees yesterday. >:( At the end, I pulled out the shop vac hose from the bottom and it was dry.