I have a sea recovery water maker with a pre filter and oil water separator. What is the technical difference between the two filters? The oil water separator looks JUST like the pre filter except it has a sock over it. Are there any other differences? I assume the sock is the oil absorbing agent so in theory shouldn't i be able to use two oil/water separators as opposed to one of each filter? I could be really off on this so please let me know what you think.