Well it means there's a red knob that let you ajust the water flow going into the skimmer...and this flow is climbing the inner tubing of the skimmer, and can easily get into the cup and fill it in minutes, even less. And once the cup is filled, well, it's a wet party on the floor.
There are more reliable skimmers, but like i said, this one is cheap..and the powerhead is a monster.
I know 2 guys who have the same skimmer as me IN A SUMP and 0 problems...also 0 nitrates.
Mine is on my tank, the sump is just too small for a 25.5" long skimmer that holds like 5 gallons