Both types of gas vents create vacuums instead of emitting the gas in its pipe under the following conditions:
- Gas packets passed to the vent are less than 1g;
- The gas surrounding the vent is different than in the pipe;
- The gas surrounding the vent is at least 900g.
The attached image shows a setup that can delete up to 27g/s (the valve closest to the pump is set to 25g/s, so the bottom two vents are not being used). If there is enough space around the vent, the surrounding gas doesn't usually get deleted, only displaced.
Create a box that encloses a 3x3 space with a gas vent in the center. Fill the box with 1kg per tile of any gas. Place a gas valve so that its output goes to the vent. Set the valve to 0.9g/s. Hook up the valve's input to a source of gas that is different from the gas in the box.