Ok, I have mine connected as the intake to a fluval 404 filter. I tossed the ugly flex tubing it came with though and have a hard plastic tube instead with an elbow. The adjustment can be a bit finicky at times, but by turning the stick thats on the top of the skimmer assembly you open up or close off the bottom water inlet. When its closed off more water is sucked off the top of the aquarium, but also too much and you draw in air. I keep mine set so that its barely skimming the top and taking in as much water in the lower inlet as possible. If its reduced the flow rate of my filter I can't tell.