Hello what you have is an MTC Pro 4500 airlift skimmer there should be and air stone preferably a limewood air stone attached to the small rigid tube that runs down the middle of the skimmer which will need to be replaced on a monthly basis minimum.water flows into the top green hose via an ehiem 1048 pump pump or similar device.as water is falling through the skimmer to drain out the bottom tube back into the sump.The air flow from the lime wood air stone is lifting the debris in the form of foam.the container on the left is a waste collector for the skimate.What you have is old school technology but still works great aslong as you don't mind changing the air stones everymonth for the best efficiency.If i did not explain this easily enough for you to understand send a P.M. will give you my number.