Not nearly enough pull for that to happen. That would take quite a bit of vacuum to get it from the bottom of the can, through the can, and out. Whereas if it was just sitting in a honeycomb it could easily be pulled through with airflow. Being on the valve side it pushes it through the comb allowing it to condense on it and drip down. If it was allowed to flow through and the comb was on the intake side it would filter by pulling, and would be far less efficient in removing it from the air and would just eventually be pulled through. There wouldn't be any time for it to condense and drip back down.But doesn't that mean, if oil accumulates at the bottom the intake can suck the oil up again.