Reef Octopus BH1000 skimmer HOB help
Needs to be primed. Take the silencer off and put your finger over the end of the clear-ish air tubing... The water level should rise a bit and then release your finger. The put silencer back on. Should be good after that.
If that doesn't work, then you may need to actually suck the airline like a straw to get the water level to raise, and then release.
That also brings up another basic thought of how high the water level is in the tank. If it's too low, it may not have enough head pressure to suck the water up. Food for thought.