if it's the pump I'm thinking of, it's a 2x2 entity with an input pipe and output pipe.
if you turn on the legacy setting to allow them, they can be used to create Lithia/pure/normal water.
They're also used to (un)barrel fluids, which is why there's an input pipe.
Those I was going to replace the graphics on.
The gas venting pump is what it says, it vents gas. You pump a gas into it (Oxygen, Hydrogen, Chlorine etc) that you don't want, and it disapears, creating (or cleaning) pollution, based on the gas.