Submerge it to the ridge on the side of the skimmer body, the one nearest the top. Plug the unit in with the venturi screw completely closed. Open it 2.5 to 3 full turns. Wait one week, it takes at least one week for the skimmer to break in and to give any accurate represetation of performance. The you can tweek it up or down in 1/4 turn increments until the skimmate is a tea color. It will be lighter than what many other skimmers produce and this has to do with the design leaning towards removal of cellulose and plant organics and less towards albumin. The skimmate usually has a chilli pepper like smell from the capsaicin in the algaes and not the really rotten smell of other skimmate, it will definitely be lighter, green to dark tea in color. The riser tube foam column is not of much consequence it is what the resulting skimmate is like that is important.