[JSeery]

Well, it is not exactly gravity drain. The canister is pressurized because of the inflow of oil through the restrictor. But, the flow is being restricted. The grain holes see the same pressure in the canister, but should be capable of twice the flow out. Not sure how to calculate the canister pressure without thinking about it a bit, but if flow out can approach double the flow in there should be a lower pressure in the canister vs oil supple pressure. Regardless, there will be some pressure in there and the lid needs a good seal. Also, the filter material will restrict the flow and increase the pressure around it. If there was not a pressure differential the oil would not move through the filter. Another reason for the outlet having twice the flow as the inlet.