NWB 110

I have a reef octopus nwb 110. In the manual it indicates that the water outlet pipe cannot be covered. What I’m gathering from this is that the water outlet pipe cannot be completey submerged underwater. How about if the water is covering just a ¼” of the water outlet pipe. Is that ok or does the water outlet pipe has to be completely above the water line to function properly. I’m just a bit confuse about this.